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<<<EngineeringDrawing>>>
BASICSOFEngineeringdrawing

Creatingadrawing
Drawinginstrumentsareusedtodrawstraightlines,circles,andcurvesaccuratelyconcisely

Thedrawingtoolsarelikedrawingboard,minidrafter,instrumentboxcontainingcompass,divideretc,..setsquares,protractor,frenchcurves,
drawingsheet,pencils,erasers.....

DRAWINGSTANDARDS

Drawingstandardsaresetofrulesthatgovernhowthetechnicaldrawingsarerepresented
theseareusedsothateveryonecancommonlyunderstandthemeaningofdrawnpicture

Drawingsheet
wehavemanytypesandsizesofdrawingsheets..likeA4,A3,A2,A1,A0etc

whileinthedrawingsheet..firstwehavetodrawborderlinesandtitleboxandthenwehavetostartdrawing

lettering
letteringandnumberingshouldbeinaperfectmanner..forexampleinthisfigure..theupperandlowercaselettersareneatlydraw

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linesanditstypes
basicallylineswhichareusedintherepresentationofthediagramsareofmainly4typestheyare

Visibleline:representfeaturesthatcanbeseeninthecurrentview
DimensionlineExtensionlineLeaderline:indicatethesizesandlocationoffeatures
Hiddenline:representfeaturesthatcannotbeseeninthecurrentview
Centerline:representssymmetry,pathofmotion,centersofcircles,axisofaxisymmetricalparts

Inthiswayweusedifferenttypesoflinesinthedrawing

BasicEngineeringDrawingProjection

Engineersareconfrontedwiththetaskofcommunicatingthedesign,developmentandstructuresofmachinestomanufacturersandbuilders.Theshapeandsizeof
variouspartsofamachineanditsstructuremustberecordedonplanesheetsinasystematicwayforcommunication.Thepictorialviewoftheobjectdoesnotcarryallthe
details,especiallytheinnerdetailsandcorrectshapeofcomplicatedparts.Differentmethods,therefore,areimpliedfordescribingtheexactshapebasedonthe
projectorsdrawnbyengineers.
PrincipleofProjection
Ifstraightlinesaredrawnfromvariouspointsonthecontourofanobjecttomeetaplane,theobjectissaidtobeprojectedonthatplane.Thefigureformedbyjoining,in
correctsequence,thepointsatwhichtheselinesmeettheplane,iscalledtheprojectionoftheobject.Thelinesfromtheobjecttotheplanearecalledprojectors.

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ProjectiononaSinglePlane
Ifstraightlinesaredrawnfromthevariouspointsonthecontourofanobjecttomeetaplane,thefigureobtainedontheplaneiscalledtheProjectionoftheobject.The
objectissaidtobeprojectedontheplane.Inotherwords,wecansaythattheprojectionofanobjectonaplaneistheshadowoftheobjectontheplaneshowingeach
andeveryedgelineoftheobject.Theimaginarylinesdrawnfromtheobjecttotheplanearecalledprojectorsorprojectionlines.Theplaneonwhichtheprojectionofthe
objectistakeniscalledplaneofprojection.Supposeanobjectisplacedinfrontofascreenandlightthrownontheobject(assumingthelightraystobeparalleltoeach
otherandperpendiculartothescreen)thenatrueshadowoftheobjectisobtainedonthescreen.Thisshadowistheprojectionontheobjectontheplaneofscreen
showingthecontourlineoftheobject.
TypesofProjections
Theprojectionsareclassifiedaccordingtothemethodoftakingtheprojectionontheplane.Aclassificationofprojectionisshownbelow:
FactorsonWhichTypeofProjectionDepends
Differentviewsofanobjectcanbedrawnbyprojections.Thuseverydrawingofanobjectwillhavefourthingsonwhichprojectiondepends
(a)Object,
(b)Projectors,
(c)Planeofprojection,and
(d)Observerseyeorstationpoint.
MethodsofProjection
Inengineeringdrawingfollowingfourmethodsofprojectionarecommonlyused,theseare:
(a)Isometricprojection
(b)Obliqueprojection

(c)Perspectiveprojection
(d)Orthographicprojection
Intheabovemethods(a),(b)and(c)representtheobjectbyapictorialviewasanobserverseesit.Inthesemethodsofprojectionathreedimensionalobjectis
representedonaprojectionplanebyoneviewonly.Whileintheorthographicprojectionanobjectisrepresentedbytwoorthreeviewsonthemutualperpendicular
projectionplanes.Eachprojectionviewrepresentstwodimensionsofanobject.Forthecompletedescriptionofthethreedimensionalobject,atleasttwoorthreeviews
arerequired.OrthographicprojectioncomesunderthecategoryofNonPictorialDrawing.
OrthographicProjections
Thewordorthographicmeansstraightdescription.Thestraightdescriptionherestandsfortheparallelprojectorsfromtheobjecttoinfinity.Ifaperpendicularpictureplane
isinsertedbetweentheprojectors,apictureisformedhavingthesameshapeandsizeasthatoftheobject.IfanobserveratpositionAmovestoinfinity,theprojectorsto
hiseyesbecomesparalleltotheobjectandheobservesthesameshapeandsizeasthatoftheobject.Theviewsoformedisknownastheorthographicprojection.
Similarly,theparallelprojectorsshallformthepicturesontherespectivepictureplanesfromthepositionsBandC.Usuallytwoviewsaresufficientforsimpleobjects,but
thehelpofthreeormoreviewsisnecessaryforcomplicatedobjects.ThesepictureplanesaremutuallyperpendiculartoeachotherandareknownasPrincipalPlanesof
projectors,namedHorizontalPlane(HP),VerticalPlane(VP)andProfilePlane(PP).
MethodsofOrthographicProjection
Thetwomethodsofprojectionsare:
(a)Firstangleprojections
(b)Thirdangleprojections
Figure3showsfourquadrantsformedbytheintersectionofhorizontalandverticalplanes.Theintersectinglineoftheplanesiscalledthecoordinateaxis.Therevolving
directionofthehorizontalplaneshowsthatquadrantsIandIIIareopenbutIIandIVquadrantsbecomeclosedwhenthehorizontalplanecoincideswiththevertical
plane.Itisobviousthattheclosedquadranthasnouseforthepurposeofprojectorsastheviewstakenonthesewilloverlap.
FirstAngleProjections.ThismethodofprojectionispopularinEurope,especiallyinBritain.BureauofIndianStandardhasalsorecommendeditnow.Figure4showsan
objectplacedinthefirstquadrant.ParallelprojectorsinthedirectionA,fromtheobject,formsapictureontheverticalplane(VP)whichisknownasFrontVieworFront
Elevation.Similarly,parallelprojectorsfromthedirectionofBformsthepictureonthehorizontalplane(HP),knownasTopVieworPlan.Amutuallyperpendicularplane
tobothHPandVP,knownasprofileplane(PP)alsoreceivesprojectorsfromtheobjectfromthedirectionC.TheviewontheprofileplaneisknownasSideVieworSide
Elevation.Thethreeplanescontainingtheviewsarethenopenedonaplane.Thesymboloffirstangleisshowninbelow.
Althoughtwoorthreeviewsareenoughtorevealanobject,theprojectorsfromsixdirectionsoftheobjectinthefirstangleareshown,ifnecessary.Theviewsaretobe
shownsymmetrically.Theviewfromthetop(DirectionB)placedunderneath.Theviewfromthefront(DirectionA)isplacedinthecentre.Theviewfromtheleftside
(DirectionC)isplacedontherightsideofviewA.Theviewfromtherightside(DirectionD)isplacedontheleftside.Theviewfromthebottom(directionE)isplacedon
thetopasEview.Theviewfromtherear(DirectionF)maybeplacedontherightorleftsideofCorDviews.
ThirdAngleProjections.ThissystemofprojectionisknownastheAmericansystem.Theobjectisplacedinthe3rdquadrant.Theplanesareimaginedtobemadeof
transparentmaterial,sayaglassbox.Thefrontwalloftheboxisassumedtobehingedtotheotherwallsasshowninthefigure.Theparallelprojectorsinallthesix
directionsformrespectiveviewsonthewallsoftheboxservingaspictureplanes.Thehingedwallsoftheboxareopenedandlaiddownonaplane.Theplacementof
variousviewsareinasystematicway.TheviewfromthetopisplacedabovetheFrontView(FV).TheviewfromtherighthandsideisplacedontherightsideofFV.The
viewfromlefthandsideisplacedontheleftsideofFV.TheviewfrombottomisplacedunderneaththeFV.Theviewfromtherearmaybeplacedontherightortheleftof
thesideviews.Thesymbolforthethirdangleisgivenbelow.
ComparisonofFirstAngleProjectionandThirdAngleProjectionmethod
Sl
FirstAngleProjectionMethod ThirdAngleProjectionMethod
No.
Theobjectisassumedtobekeptinthe
1 Theobjectiskeptinthefirstquadrant.
thirdquadrant.
Theobjectliesbetweentheobserverand Theplaneofprojectionliesbetweenthe
2
theplaneofprojection. observerandtheobject.
Theplaneofprojectionisassumedtobe Theplaneofprojectionisassumedto
3
nontransparent. betransparent
Inthismethod,whentheviewsaredrawn Inthismethod,whentheviewsare
intheirrelativepositions,Plan(Topview) drawnintheirrelativepositions,Plan
comesbelowtheelevation(Frontview),
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4 theviewoftheobjectasobservedfrom comesabovetheelevation,lefthand
theleftsideisdrawntotherightof sideviewisdrawntothelefthandsideof
elevation. theelevation.

Thismethodofprojectionisnow
Thismethodofprojectionisusedin
5 recommendedbytheBureauofIndian
U.S.Aandalsoinothercountries.
Standardsfrom1991.
BasicEngineeringDrawingLettering

Writingoftitles,dimensions,notes,andotherimportantparticularsonadrawingiscalledlettering.Letteringisanimportantpartofadrawing.Howeveraccurateandneat
adrawingmaybedrawn,itsappearanceisspoiledandsometimes,itsusefulnessisimpairedbypoorlettering.Letteringshould,therefore,bedoneproperlyinclear,
legibleanduniformstyle.Itshouldbeinplainandsimplestylesothatitcouldbedonefreehandandspeedily.
StyleofLetteringTherearevariousformsofalphabetsusedintheartofletteringandeachtypeisusedforsomeparticularpurpose.OldRomanstyleistheparentof
allthesestyles.Itisthebasicstandardforarchitectsandartists.AvariationofthisstyleisknownasModernRomanusedbycivilengineers,inmapsandphotographical
drawings.ThesimplifiedformscalledCommercialGothicareusedalmostexclusivelyforworkingdrawings.Gothiclettersareelementarystrokesofevenwidth.Roman
lettershaveelementarystrokesaccentedorconsistingofheavyandlightlines.AllslantinglettersareclassifiedasItalics.
TypesofLetteringLetteringmaybedrawninvarioustypes.Thesearegivenbelow:
(a)AccordingtotheHeight
(i)LetteringA
(ii)LetteringB
InletteringAtype,theheightofthecapitalletterisdividedinto14parts,whileinletteringBtype,itisdividedinto10parts.Theheightoflettersandnumeralsfor
engineeringdrawingaregenerallyintherangeof2.5,3.5,5,7,10,14and20mmaccordingtothesizeofdrawing.
Table1LetteringA(d=h/14)
Characteristic Ratio Dimensions(mm)

Letteringheight


(14/14)h 2.5 3.5 5 7 10 14 20
Heightofcapitalsh

Heightoflowercaselettersc
(10/14)h 2.5 3.5 5 7 10 14
(2/14)h 0.35 0.5 0.7 1 1.4 2 2.8
Spacingbetweencharactersa

Minimumspacingofbaselinesb (20/14)h 3.5 5 7 10 14 20 28
Minimumspacingbetweenwordse
(6/14)h 1.05 1.5 2.1 3 4.2 6 8.4
Thicknessoflinesd (1/14)h 0.18 0.25 0.35 0.5 0.7 1 1.4

Table2LetteringB(d=h/10)
Characteristic Ratio Dimensions(mm)


Letteringheight

(10/10)h
2.5 3.5 5 7 10 14 20
Heightofcapitalsh

Heightoflowercaselettersc
2.5 3.5 5 7 10 14
(7/10)h
(2/10)h 0.5 0.7 1 1.4 2 2.8 4
Spacingbetweencharactersa

Minimumspacingofbaselinesb (14/10)h 3.5 5 7 10 14 20 28
Minimumspacingbetweenwordse
(6/10)h 1.5 2.1 3 4.2 6 8.4 12
Thicknessoflinesd (1/10)h 0.25 0.35 0.5 0.7 1 1.4 2

(b)AccordingtotheProportionofWidthandHeight
(i)NormalLetters.Normallettershaveusualheightandwidthandareusedforgeneralpurposewritteninusualspace.
(ii)CompressedorCondensedLetters.Compressedorcondensedlettersarethosewhicharewrittennarrowintheirproportionofwidthtoheight,i.e.heightofthese
lettersismorethanthewidth.Theseareusedwhenthespaceislimited.
(iii)ExtendedLetters.Extendedlettersarethosewhicharewrittenwideintheirproportionofwidthtoheight,i.e.heightoftheselettersislessorequaltothewidth.
(c)AccordingtotheStemThickness.Lettersalsovaryinthethicknessofthestemsorstrokes.Lettershavingverythinstemsarecalledlightface,whilethosehavingheavy
stemsarecalledboldface.
LIGHTFACE
BOLDFACE
LightandBoldFaceLetters
(d)AccordingtotheStrokeofPencil

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(i)SingleStrokeLetters.Thethicknessofthelinesofthesinglestrokelettersisobtainedinonestrokeofthepencil.Thisisthereasonwhythesearecalledsinglestroke
letters.Theselettersbeingsimpleareusuallyemployedinmostoftheengineeringdrawings.Singlestrokelettersareoftwotypes:(i)vertical(ii)inclined.Bothvertical
andinclinedlettersandnumeralsaresuitableforgeneraluse.Onecanresorttoanyofthesetwo,dependinguponconvenience.Thelinesoftheinclinedlettersare
drawnatanapproximateinclinationof75Ototheright.
(ii)DoubleStrokeLetters.Thethicknessofthelinesofthedoublestrokeletterscannotbeobtainedbyasinglestrokeofpencilandhence,twostrokesofthepencilare
used.Thisisthereasonwhythesearecalleddoublestrokeletters.Thelettersandnumeralshaveuniformthicknessinthisstyle.Theratioofthicknessandheightof
lettersis1:10and1:14.
Agoodstyleofsinglestrokeletteringshouldaimat:
(a)UniformityofThickness.Conicalpointpencilisusedforuniformity.Pencilshouldnotbetoosharpasitwouldpierceintothesurfaceofthedrawingpaper.
(b)UniformityofSize.Thewidthofthestrokeofthepencilorpenistobesameasthewidthoftheletter.Lightguidelinesforbothtopandbottomoflettersshouldalways
bedrawnwithasharppencil.
(c)UniformityofStyle.Oneofthetwostyles,verticalorinclined,shouldbeused.Verticalletteringisusuallypreferred.Bothverticalandinclinedlettersarestandardand
thetechniciansshouldusethemaccordingtotheirpracticeandconvenience.
(d)UniformityofSpacing.Uniformityinspacingofletters,whethertheyareverticalorinclined,isamatterofequalizingthespacesbetweenalphabets,words,lines,etc.
Thebackgroundareabetweenletters,notonlythedistancebetweenthem,shouldbeapproximatelyequal.
(e)UniformityofShape.Theshapeofalltheletters,irrespectiveofthestylesortypesused,shouldbeuniform.Ifinclinedlettersareused,allofthemmusthavethesame
inclinationandshouldbeinclinedtowardstherighthandside.

EngineeringDrawingAndWorkshopDrawing


Engineeringdrawingisalanguagewhichisunderstoodthroughouttheworldbyengineersandfabricators.Otherlanguagesmayfailtodescribethesize,shape,physical
aspects,innerdetails,finish,etc.,buttheengineerslanguageknownasEngineeringDrawingneverfails.Themostintricateassemblieswiththeirvariouscomplicated
partscanbeeasilyrepresentedbyengineeringgraphics.Therearevarioustypesofengineeringdrawingsandallhaveonesimplepurpose,i.e.thecommunicationof
ideastoothers.ThedrawingsusedforcommunicatingtheideasofthedesignengineertotheproductionengineerandtechniciansisknownasWorkshopDrawing.
EngineeringDrawingAdrawingPreparedbyanengineer,foranengineeringpurposeisknownasanengineeringdrawing.Itisthegraphicrepresentationofphysical
objectsandtheirrelationship.Itisprepared,basedoncertainbasicprinciples,symbolicrepresentations,standardconventions,notations,etc.Itistheonlyuniversal
meansofcommunicationusedbyengineersandtechnicians.
PictorialDrawingEverypersoncannotunderstandtheorthographicprojection.Itsexecutionrequiresathoroughunderstandingoftheprinciplesofprojectionandits
readingrequiresagoodpracticeofconstructiveimagination.Wecandescribetheshapeofajobbymeansofpictorialdrawingalso,whichcanbeunderstoodquiteeasily.
Pictorialdrawingisthedrawingofapictureingraphiclanguageofengineers,torepresentarealthingbymeansofpictureviews.Itshowstheappearanceoftheobjectby
oneviewonly.Followingthreemethodsofpictorialprojectionsarecommonlyusedinengineeringdrawing:
(a)Isometricprojection
(b)Obliqueprojection
(c)Perspectiveprojection
IsometricProjection
Atrainedeyeandgoodimaginationwillbeabletounderstandthethreedimensionsofanobject.Severalorthographicviewsondifferentplanesaretobedrawnto
understandfullyanobject.Butinisometricprojection,onlyoneviewonaplaneissufficienttorepresentanobjectinitsrealisticappearance.Anyonecanunderstandby
lookingataviewwhatthejobisbyisometricprojection.
Isometricprojectionisatypeofpictorialprojection.Isometricmeansequalmeasure.Inthisisometricprojection,alltheplanesurfacesandtheedgesformedofthese
planesurfacesshouldbeequallyinclinedtothemetricplane.Metricplaneisthesamehorizontalplanewhichisusedinorthographicprojection.
Torepresentthethreedimensions(length,breadthandheight)oftheobject,therearethreeaxesknownasISOMETRICAXES.Tostartanisometricdrawing,areference
line(horizontalline)andthethreeaxes(X,YZ)aredrawnbytakinganangleof30fromthereferencehorizontallineasdrawninFig7.2.Zaxisisaverticallinetothe
horizontallinedrawnfromintersectionpointofXandYaxes.
ObliqueProjection.
Obliqueprojectionmaybeillustratedindifferentways,accordingtothechoiceofaxes,lengthofinclinedsideanddirectionoflookingtheside.Ascomparedwith
isometricprojection,inobliqueprojection,onesideoftheobjectishorizontal,secondsideisverticalandthethirdsideisinclinedat30Oor45Otothehorizontal.The
lengthsofthehorizontalandverticalsidesareequaltotheactuallengths,butthelengthoftheinclinedsideistakenasthreefourthorhalfoftheactuallength.
Inobliqueprojection,anobjectisplacedwithitsfrontfaceparalleltoaverticalplaneofprojectionandthevisualraysparalleltoeachotherpiercetheplaneofprojection
obliquely(Obliquemeansinclined).Theprojectionrepresentsthefrontfaceoftheobjectinitstrueshapeandsize.Therestoftheobjectisnotprojectedtrueinitsshape
andsize.Boththeisometricandobliqueprojectionsarethemethodsofrepresentingtheobjectpictorially.Buttheobliqueprojectionispreferabletotheisometric
projectioninrepresentingtheobjectsofcircularshapes,becausethefrontfaceisinactualshapeandsize.Itisnotdistorted.
PerspectiveProjection.
Perspectiveprojectionorperspectivedrawingistherepresentationofanobjectonaplanesurface,calledthepictureplane,asitwouldappeartotheeye,whenviewed
fromafixedposition.Itmayalsobedefinedasthefigureformedonthepictureplanewhenvisualraysfromtheeyetotheobjectcutthepictureplane.Perspectiveis
mainlyusedinarchitecture.Bymeansofperspective,thearchitectureisabletoshowhowanobjectwouldappearwhenconstructed.
NonPictorialDrawing
Itisnotalwayspossibletovisualizetheobjectmerelybylookingatthedrawing.Itrequiresthehelpofcertainrulesandconventionofengineeringdrawing.Itcanbe
charts,maps,layouts,aerialphotographsandorthographicprojections.

WorkshopDrawing
Thepurposeofaworkshopdrawingistoconveytheinstructionsofthedesignertothemechanicconcerned,insuchamannerthattheworktobedonecanbecompleted
withaccuracyandasrapidlyaspossible.Thedrawingwillshowallnecessarymeasurements,whichareexpressedclearlywithouttheneedforanycalculation.Thelimits
ofaccuracyortheclassoffitandtherawmaterialsfromwhichthepartsaretobemade,arealsoindicated.

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Thedrawingmaynotbeofactualsize,butforconveniencemaybemadelargerorsmallerthantheactualjob,i.e.itwillbedrawntoscale.Thescaleisindicatedinthetitle
block.Owingtousageandthepossibilityofbeingtorn,itisundesirablethattheoriginaldrawingshouldbeusedintheworkshop.Instead,anumberofprintsare
reproduced.
TypesofWorkshopDrawing
Therearethreetypesofworkshopdrawing:
(a)DetailDrawing.Thistypeofdrawingprovidesallnecessarydimensionsandworkinginstructionsfortheproductionofanitem,e.g.onepartofahydrauliccomponent.
(b)AssemblyDrawing.Thistypeofdrawingshowsthecomponentorassemblyinanassembledstate,e.g.theassemblyofthevariouspartsofahydrauliccomponent.
(c)GeneralArrangementDrawing.Thistypeofdrawingshowsanumberofcomponentsinanassembledconditiontoformaselfcontainedunit,e.g.thecomplete
hydraulicsystemofanaircraft.
RequirementofaGoodWorkshopDrawing
Workshopdrawingsareintendedtoconveytherequirementsofthedesignertothetradesmaninsuchawaythattheintendedworkcanbecarriedoutaccuratelyand
rapidly.Tofacilitateitsreading,agoodworkshopdrawingshouldsatisfythefollowingrequirements:
(a)Itshouldshowallthenecessarymeasurementswithoutsuperfluousdataorrepetition.
(b)Itshouldnotentailanykindofcalculations.
(c)Clearlyindicatetherawmaterialfromwhichpartsaretobemade.
(d)Clearlyindicatethelimitofaccuracyorclassoffitasapplicable.
(e)Provideakeytomachiningandothersymbols.
(f)Anyotherinformationnotprovidedintheaboveclausesthatmayberequiredforsatisfactorycompletionofwork.
WorkshopNotes
Theuseofproperlycomposednotesoftenaddsclaritytothepresentationofdimensionalinformationinvolvingspecificoperations.Notesarealsousedtoconvey
supplementaryinstructionaboutthekindofmaterial,kindoffit,degreeoffinish,etc.Itisagoodpracticetospecifyinformationrepresentingaspecifictooloperationora
seriesoftooloperationsbynotesratherthanbyfigureddimensions.Brevityinformisdesirablefornotesofgeneralinformationorspecificinstructions.
Introduction
Oneofthebestwaystocommunicateone'sideasisthroughsomeformofpictureordrawing.Thisisespeciallytruefortheengineer.Thepurposeofthisguideistogive
youthebasicsofengineeringsketchinganddrawing.
Wewilltreat"sketching"and"drawing"asone."Sketching"generallymeansfreehanddrawing."Drawing"usuallymeansusingdrawinginstruments,fromcompassesto
computerstobringprecisiontothedrawings.
Thisisjustanintroduction.Don'tworryaboutunderstandingeverydetailrightnowjustgetageneralfeelforthelanguageofgraphics.
WehopeyouliketheobjectinFigure1,becauseyou'llbeseeingalotofit.Beforewegetstartedonanytechnicaldrawings,let'sgetagoodlookatthisstrangeblockfrom
severalangles.
Figure1AMachinedBlock

IsometricDrawing
Therepresentationoftheobjectinfigure2iscalledanisometricdrawing.Thisisoneofafamilyofthreedimensionalviewscalledpictorialdrawings.Inanisometric
drawing,theobject'sverticallinesaredrawnvertically,andthehorizontallinesinthewidthanddepthplanesareshownat30degreestothehorizontal.Whendrawn
undertheseguidelines,thelinesparalleltothesethreeaxesareattheirtrue(scale)lengths.Linesthatarenotparalleltotheseaxeswillnotbeoftheirtruelength.
Figure2AnIsometricDrawing

Anyengineeringdrawingshouldshoweverything:acompleteunderstandingoftheobjectshouldbepossiblefromthedrawing.Iftheisometricdrawingcanshowall
detailsandalldimensionsononedrawing,itisideal.Onecanpackagreatdealofinformationintoanisometricdrawing.However,iftheobjectinfigure2hadaholeon

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thebackside,itwouldnotbevisibleusingasingleisometricdrawing.Inordertogetamorecompleteviewoftheobject,anorthographicprojectionmaybeused.
OrthographicorMultiviewDrawing
Imaginethatyouhaveanobjectsuspendedbytransparentthreadsinsideaglassbox,asinfigure3.
Figure3Theblocksuspendedinaglassbox

Thendrawtheobjectoneachofthreefacesasseenfromthatdirection.Unfoldthebox(figure4)andyouhavethethreeviews.Wecallthisan"orthographic"or
"multiview"drawing.
Figure4Thecreationofanorthographicmultiviewdrawing

Figure5showshowthethreeviewsappearonapieceofpaperafterunfoldingthebox.
Figure5Amultiviewdrawinganditsexplanation

Whichviewsshouldonechooseforamultiviewdrawing?Theviewsthatrevealeverydetailabouttheobject.Threeviewsarenotalwaysnecessaryweneedonlyas
manyviewsasarerequiredtodescribetheobjectfully.Forexample,someobjectsneedonlytwoviews,whileothersneedfour.Thecircularobjectinfigure6requires
onlytwoviews.
Figure6Anobjectneedingonlytwoorthogonalviews

Dimensioning
Figure7Anisometricviewwithdimensions

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Wehave"dimensioned"theobjectintheisometricdrawinginfigure7.Asageneralguidelinetodimensioning,trytothinkthatyouwouldmakeanobjectanddimensionit
inthemostusefulway.Putinexactlyasmanydimensionsasarenecessaryforthecraftspersontomakeitnomore,noless.Donotputinredundantdimensions.Notonly
willtheseclutterthedrawing,butif"tolerances"oraccuracylevelshavebeenincluded,theredundantdimensionsoftenleadtoconflictswhenthetoleranceallowances
canbeaddedindifferentways.
Repeatedlymeasuringfromonepointtoanotherwillleadtoinaccuracies.Itisoftenbettertomeasurefromoneendtovariouspoints.Thisgivesthedimensionsa
referencestandard.Itishelpfultochoosetheplacementofthedimensionintheorderinwhichamachinistwouldcreatethepart.Thisconventionmaytakesome
experience.
Sectioning
Therearemanytimeswhentheinteriordetailsofanobjectcannotbeseenfromtheoutside(figure8).
Figure8Anisometricdrawingthatdoesnotshowalldetails

Wecangetaroundthisbypretendingtocuttheobjectonaplaneandshowingthe"sectionalview".Thesectionalviewisapplicabletoobjectslikeengineblocks,where
theinteriordetailsareintricateandwouldbeverydifficulttounderstandthroughtheuseof"hidden"lines(hiddenlinesare,byconvention,dotted)onanorthographicor
isometricdrawing.
Imagineslicingtheobjectinthemiddle(figure9):
Figure9"Sectioning"anobject

Figure10Sectioningtheobjectinfigure8

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Takeawaythefronthalf(figure10)andwhatyouhaveisafullsectionview(figure11).
Figure11Sectionedisometricandorthogonalviews

Thecrosssectionlookslikefigure11whenitisviewedfromstraightahead.
DrawingTools
Toprepareadrawing,onecanusemanualdraftinginstruments(figure12)orcomputeraideddraftingordesign,orCAD.Thebasicdrawingstandardsandconventions
arethesameregardlessofwhatdesigntoolyouusetomakethedrawings.Inlearningdrafting,wewillapproachitfromtheperspectiveofmanualdrafting.Ifthedrawing
ismadewithouteitherinstrumentsorCAD,itiscalledafreehandsketch.
Figure12DrawingTools

"Assembly"Drawings
Anisometricviewofan"assembled"pillowblockbearingsystemisshowninfigure13.Itcorrespondscloselytowhatyouactuallyseewhenviewingtheobjectfroma
particularangle.Wecannottellwhattheinsideofthepartlookslikefromthisview.
Wecanalsoshowisometricviewsofthepillowblockbeingtakenapartor"disassembled"(figure14).Thisallowsyoutoseetheinnercomponentsofthebearingsystem.
Isometricdrawingscanshowoverallarrangementclearly,butnotthedetailsandthedimensions.
Figure13Pillowblock(Freehandsketch)

Figure14DisassembledPillowblock

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CrossSectionalViews
Acrosssectionalviewportraysacutawayportionoftheobjectandisanotherwaytoshowhiddencomponentsinadevice.
Imagineaplanethatcutsverticallythroughthecenterofthepillowblockasshowninfigure15.Thenimagineremovingthematerialfromthefrontofthisplane,asshown
infigure16.
Figure15PillowBlock Figure16PillowBlock

Thisishowtheremainingrearsectionwouldlook.Diagonallines(crosshatches)showregionswherematerialshavebeencutbythecuttingplane.
Figure17Section"AA"

Thiscrosssectionalview(sectionAA,figure17),onethatisorthogonaltotheviewingdirection,showstherelationshipsoflengthsanddiametersbetter.Thesedrawings
areeasiertomakethanisometricdrawings.Seasonedengineerscaninterpretorthogonaldrawingswithoutneedinganisometricdrawing,butthistakesabitofpractice.

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Thetop"outside"viewofthebearingisshowninfigure18.Itisanorthogonal(perpendicular)projection.Noticethedirectionofthearrowsforthe"AA"cuttingplane.
Figure18Thetop"outside"viewofthebearing

HalfSections
Ahalfsectionisaviewofanobjectshowingonehalfoftheviewinsection,asinfigure19and20.
Figure19Fullandsectionedisometricviews

Figure20Frontviewandhalfsection

Thediagonallinesonthesectiondrawingareusedtoindicatetheareathathasbeentheoreticallycut.Theselinesarecalledsectionliningorcrosshatching.Thelines
arethinandareusuallydrawnata45degreeangletothemajoroutlineoftheobject.Thespacingbetweenlinesshouldbeuniform.
Asecond,rarer,useofcrosshatchingistoindicatethematerialoftheobject.Oneformofcrosshatchingmaybeusedforcastiron,anotherforbronze,andsoforth.More
usually,thetypeofmaterialisindicatedelsewhereonthedrawing,makingtheuseofdifferenttypesofcrosshatchingunnecessary.
Figure21Halfsectionwithouthiddenlines

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Usuallyhidden(dotted)linesarenotusedonthecrosssectionunlesstheyareneededfordimensioningpurposes.Also,somehiddenlinesonthenonsectionedpartof
thedrawingsarenotneeded(figure12)sincetheybecomeredundantinformationandmayclutterthedrawing.
SectioningObjectswithHoles,Ribs,Etc.
Thecrosssectionontherightoffigure22istechnicallycorrect.However,theconventioninadrawingistoshowtheviewontheleftasthepreferredmethodforsectioning
thistypeofobject.
Figure22Crosssection

Dimensioning
Thepurposeofdimensioningistoprovideaclearandcompletedescriptionofanobject.Acompletesetofdimensionswillpermitonlyoneinterpretationneededto
constructthepart.Dimensioningshouldfollowtheseguidelines.

1. Accuracy:correctvaluesmustbegiven.
2. Clearness:dimensionsmustbeplacedinappropriatepositions.
3. Completeness:nothingmustbeleftout,andnothingduplicated.
4. Readability:theappropriatelinequalitymustbeusedforlegibility.

TheBasics:DefinitionsandDimensions
Thedimensionlineisathinline,brokeninthemiddletoallowtheplacementofthedimensionvalue,witharrowheadsateachend(figure23).
Figure23DimensionedDrawing

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Anarrowheadisapproximately3mmlongand1mmwide.Thatis,thelengthisroughlythreetimesthewidth.Anextensionlineextendsalineontheobjecttothe
dimensionline.Thefirstdimensionlineshouldbeapproximately12mm(0.6in)fromtheobject.Extensionlinesbegin1.5mmfromtheobjectandextend3mmfromthe
lastdimensionline.
Aleaderisathinlineusedtoconnectadimensionwithaparticulararea(figure24).
Figure24Exampledrawingwithaleader

Aleadermayalsobeusedtoindicateanoteorcommentaboutaspecificarea.Whenthereislimitedspace,aheavyblackdotmaybesubstitutedforthearrows,asin
figure23.Alsointhisdrawing,twoholesareidentical,allowingthe"2x"notationtobeusedandthedimensiontopointtoonlyoneofthecircles.
WhereToPutDimensions
Thedimensionsshouldbeplacedonthefacethatdescribesthefeaturemostclearly.Examplesofappropriateandinappropriateplacingofdimensionsareshownin
figure25.
Figure25Exampleofappropriateandinappropriatedimensioning

Inordertogetthefeelofwhatdimensioningisallabout,wecanstartwithasimplerectangularblock.Withthissimpleobject,onlythreedimensionsareneededto
describeitcompletely(figure26).Thereislittlechoiceonwheretoputitsdimensions.
Figure26SimpleObject

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Wehavetomakesomechoiceswhenwedimensionablockwithanotchorcutout(figure27).Itisusuallybesttodimensionfromacommonlineorsurface.Thiscanbe
calledthedatumlineofsurface.Thiseliminatestheadditionofmeasurementormachininginaccuraciesthatwouldcomefrom"chain"or"series"dimensioning.Notice
howthedimensionsoriginateonthedatumsurfaces.Wechoseonedatumsurfaceinfigure27,andanotherinfigure28.Aslongasweareconsistent,itmakesno
difference.(Wearejustshowingthetopview).
Figure27Surfacedatumexample

Figure28Surfacedatumexample

Infigure29wehaveshownaholethatwehavechosentodimensionontheleftsideoftheobject.Thestandsfor"diameter".
Figure29Exampledofadimensionedhole

Whentheleftsideoftheblockis"radiuses"asinfigure30,webreakourrulethatweshouldnotduplicatedimensions.Thetotallengthisknownbecausetheradiusofthe
curveontheleftsideisgiven.Then,forclarity,weaddtheoveralllengthof60andwenotethatitisareference(REF)dimension.Thismeansthatitisnotreallyrequired.

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Figure30Exampleofadirectlydimensionedhole

Somewhereonthepaper,usuallythebottom,thereshouldbeplacedinformationonwhatmeasuringsystemisbeingused(e.g.inchesandmillimeters)andalsothescale
ofthedrawing.
Figure31Exampleofadirectlydimensionedhole

Thisdrawingissymmetricaboutthehorizontalcenterline.Centerlines(chaindotted)areusedforsymmetricobjects,andalsoforthecenterofcirclesandholes.Wecan
dimensiondirectlytothecenterline,asinfigure31.Insomecasesthismethodcanbeclearerthanjustdimensioningbetweensurfaces.

Engineeringdrawingabbreviationsandsymbols
FromWikipedia,thefreeencyclopedia


Engineeringdrawingabbreviationsandsymbolsareusedtocommunicateanddetailthecharacteristicsofanengineeringdrawing.Thislistincludesabbreviations
commontothevocabularyofpeoplewhoworkwithengineeringdrawingsinthemanufactureandinspectionofpartsandassemblies.
Technicalstandardsexisttoprovideglossariesofabbreviations,acronyms,andsymbolsthatmaybefoundonengineeringdrawings.Manycorporationshavesuch
standards,whichdefinesometermsandsymbolsspecifictothemonthenationalandinternationallevel,ASMEstandardY14.38[1]isprobablythemostwidelyused.
Jumpto:09ABCDEFGHIJKLMNOPQRSTUVWXYZseealso
Abbreviation
Definition Description
orsymbol
09
A
AC acrosscorners Commonlyusedwhenmeasuringthecornersofahexdrive,suchasahexnut.
AF acrossflats Commonlyusedwhenmeasuringtheflatsurfacesofahexdrive,suchasahexnut.
AISI AmericanIronand TheAISIacronymiscommonlyseenasaprefixtosteelgrades,forexample,"AISI4140".TheSAEsteel
SteelInstitute gradesystemwasformerlyajointAISISAEsystem.
AlorAL aluminium
ALY alloy
AMER American ReferringtotheUnitedStates
AMS AerospaceMaterial StandardsinmaterialsscienceandengineeringmaintainedbySAEInternationalandwidelyusedin
Standards theaerospacemanufacturingindustries.
AN Aprefixforstandardhardware(cataloghardware)IDnumbers.Camefromtheeraofcirca1890s1945,
whentheU.S.ArmyandNavywereleadingthewayonproductstandardizationforlogisticsimprovement,
yieldingtheUnitedStatesMilitaryStandardssystem.TodayindustryandISOalsodoalotofthis
ArmyNavy
standardizationspecification,freeingtheU.S.DODandmilitarytodolessofit(asexplainedatUnited
StatesMilitaryStandard>Originsandevolution),althoughmanyMILstandardsarestillcurrent.(See
alsoMSandNAS.)
ANN anneal,annealed
ANSI AmericanNational
Andthemanystandardsthatitissues,forexample,ANSIZ87.1.
StandardsInstitute
APPROX[2] approximately

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AQL Thethresholdofdefectivenessthatisallowableinagroupofparts.Itistrivialtosaythatnoonewantsany
acceptablequality error,andthateveryonewantsuniformperfectionbutintherealworld,italmostneverhappens.The
level intelligencebehinddefiningAQLsisinfiguringouthowmucherroristolerablegiventhecoststhatwould
beincurredbyanyeffortstofurtherreduceitsincidence.
AR Anabbreviationusedinpartslists(PLs,LMs,BoMs)inthequantityperassemblyfieldwhenadiscrete
countisnotapplicable.Forexample,inanassemblywithaboltedjointusingfourbolts,thePLquantity
asrequired
columnwillsay"4"fortheboltPN,"4"forthenutPN,and"AR"fortheliquidthreadlockerthatwillbe
applied.
AS Aerospace 1.AerospaceStandards,technicalstandardsmaintainedbySAEInternationalandwidelyusedin
StandardsAustralian theaerospacemanufacturingindustries.StandardaerospacehardwaresometimeshastheASprefixin
Standards thecatalognumbers.2.AustralianStandards,standardsperAustralianindustry.
AS,APS, WhenonlycertaincompaniesareapprovedbytheCDAtomanufacturetheproduct(thatis,tomakewhat
APV,AV, approvedproduct thedrawingdepicts/defines),theyarecalledbynamessuchas"approvedsupplier","approvedproduct
APSL,AVL supplier,approved supplier","approvedvendor",or"approvedproductvendor".Thelistofsuchcompanies(whichusually
vendor,approved changesovertime)iscalledanAPSL,AVL,orsimilarnames.Vettingthecompaniesonthislistrequires
productsupplierlist, theCDAtoaudit(andpossiblyperiodicallyreaudit)thecompanies,whichincursanoverheadexpensefor
approvedvendorlist theCDA.Therefore,smallercompanieswilloftencitelargercompanies'listsinordertoavoidthecostof
duplicatingtheeffort.
ASA AmericanStandards
FormernameforANSI(1920s1960s).
Association
ASME AmericanSocietyof
Andthemanystandardsthatitissues,forexample,ASMEY14.5.
MechanicalEngineers
ASSYorASY assembly referringtoanassemblyofpartsratherthanjustone(sub)part("piecepart","detailpart").
ASTM FormerlytheAmerican
SocietyforTestingand
Maintainstechnicalstandards,especiallyregardingmaterialsscienceandengineeringandmetrology.
MaterialsnowASTM
International
AVG average
AWG AmericanWireGauge
B
BASIC Abasicdimensionisonethatisthetheoreticalvaluewithoutanytolerancerange.Itdoesnotserveasan
acceptancecriterion.Itisthussimilarinsomerespectstoareferencedimension.Thereasonwhyabasic
dimensiondoesnotcarryatoleranceisthatitsactualvaluewillfall(acceptably)whereveritisputbyother
features'actualvalues,wherethelatterfeaturesaretheoneswithtolerancesdefined.Acommonand
basicdimension
simpleexampleisholelocation:Ifahole'scenterpointlocationhasapositiontolerance,thenthe
centerpoint'scoordinatesdonotneed(andshouldnothave)separatetolerancesappliedtothem.Thus
theyareinsteadgivenasbasicdimensions.Inmodernpracticebasicdimensionshavearectangularbox
aroundthem,orsometimestheword"BASIC".
BCorB.C. boltcircle
BHCS buttonheadcapscrew LikeanSHCSbutwithabuttonhead.
BHN Brinellhardness

number
BoMorBOM Alsocalledalistofmaterials(LMorL/M).Overlapsalotinconceptwithapartslist(PLorP/L).Thereis
billofmaterials
noconsistentlyenforceddistinctionbetweenanL/M,aBoM,oraP/L.
BP,B/P blueprint "perB/P"="perdrawing"
BRZ bronze
BSC basicdimension Seebasicdimensioninfoabove.
C
CAD computeraided
design,computer
aided
draftingcadmium
[plating]
CAGE ACAGEcodeisauniqueidentifiertolabelanentity(thatis,aspecificgovernmentagencyorcorporation
ataspecificsite)thatisaCDA,ODA,orMFRofthepartdefinedbythedrawing.Onecorporationcanhave
Commercialand
manyCAGEcodes,ascanonegovernment,becauseeachdivision,department,andsite(campus)can
Government
haveitsownCAGEcode.ThesameCAGEcodecanchangeownersovertheyears.Forexample,a
Entity[code]
CAGEcodethatformerlyreferredtoacertainMartinMariettasitewillnowrefertoLockheedMartinatthat
samesite(althoughthebuildingsmayhavebeenreplacedandthesignagemaysaydifferentnames).
CCorCTO centretocentreon
Definescentretocentredistanceoftwofeatures,suchastwoholes.
C centres
CBN cubicboronnitride Amaterialfromwhichsomecutterinsertsaremade.
CDA TheCDAistheentity(whetheritbeacorporation,aunitofanationalmilitaryorministryofdefence,or
anotherciviliangovernmentagency)thatcurrentlyhasdesignauthorityoverthepartdesign(definition).It
maybetheentitywhofirstdesignedthepart(thatis,theODA),buttodayitisalsolikelytobeadesignated
successorentity,owingtomergersandacquisitions(M&A)activity(e.g.,ODAcompanywasboughtby
CDAcompany)contractletting(e.g.,anArmyengineeringdepartmentODAturnsoverthedesignactivity
currentdesignactivity totheprimecontractorthatmakesmostoralloftheparts,turningthatcontractorintothenew
CDA)privatization(e.g.,agovernmentprivatizesthedesignandmanufactureofmateriel,andastate
arsenal[statearmory]ODAtransfersdesignauthoritytoaprivatearmory[defensecontractor]ODA)or
patentlicensing(e.g.,apatentholdinginventor[ODA]licensesoneorseveralcompaniestomanufacture
productsusinghisintellectualproperty,inwhichcasethe"same"partcouldendupwithmultipledesign
authorities,althoughtheymaynotbeconsideredtheofficial/nominalCDA).
CERTorcert certification Forexample,certificationofmetallurgicalcontentandprocesses
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CG centerless
ground,centerless
grinding
Centermark Definesthecenterofacircleorpartialcircle.
CH chamfer
CHAM chamfer
CI castiron Nolongeracommonlyusedabbreviation.Bettertospelloutforclarity.
CLor 1.Centerline,thecentralaxisofafeature.2.Class,forexample,"paintperspecXYZrevisionCtype1
class2"maybeabbreviatedas"paintperspecXYZREVCTY1CL2"oreveninsomecases"paintper
centerlineclass
specXYZC12".(Thelatterpracticeisnotuncommonbutiscrypticforworkerswithminimaltrainingand
experience.Thefirsttwooptionsarebetterpractice.)
CNC computernumerical

control
CR Radiusofanarcorcircle,withnoflatsorreversals.Thisstrictversionofradiusdefinitionisspecifiedin
demandingapplicationswhentheformoftheradiusmustbecontrolledmorestrictlythan"justfalling
withinthedimensionaltolerancezone".ItispoorengineeringtospecifyaCRinsteadofanRsimplyonthe
controlledradius
theoryofenforcinggoodworkmanship.CRisforcriticalfeatureswhoseperformancetrulyrequiresnear
perfectgeometry.Likemostsuchcharacteristics,itspresenceincreasesthepriceofthepart,becauseit
raisesthecostsofmanufacturingandqualityassurance.
CRES corrosionresistant Largelysynonymouswithstainlesssteel,unlessspecificgrades,specs,anddistinctionsaremadeonthe
[steel] drawing.SomepeopletreatCRESasasubsetofthestainlesssteels.
CRS coldrolledsteelon
Definescentretocentredistanceoftwofeatures,suchastwoholes.
centres
C'BOREor
CBOREor counterbore

CSKor
CSINKor countersink

CTN,ctn carton
D

depth,deep,down Definesthedepthofafeature.

[2] Diameterofacircle.Inafeaturecontrolframe(FCF),thesymboltellsyouthatthetolerancezoneforthe
diameter
geometrictoleranceiscylindrical.Abbreviationsfor"diameter"include,DIA,andD.
D diameterdelta Abbreviationsfor"diameter"include,DIA,andD.Fordeltausage,seeforexample"deltanotes".
DIA[2] diameter Diameterofacircle.Abbreviationsfor"diameter"include,DIA,andD.
DIM dimension,

dimensioning
DOD,DoD [U.S.]Departmentof
SeealsoMOD.
Defense
DPD digitalproduct
AsynonymofMBD.
definition
DWG,dwg drawing Referringtotheengineeringdrawing
E
EO,ECO, Anorderfromtheengineeringdepartment(tobefollowedbytheproductiondepartmentorvendor)
ECN overriding/supersedingadetailonthedrawing,whichgetssupersededwithrevisedinformation.Also
engineeringorder
calledbyvariousothernames,suchasengineeringchangeorder(ECO),engineeringchangenotice
(ECN),drawingchangenotice(DCN),andsoon.SeealsoREV.
EQ Forexample,"104XEQSPACEDONBC"means"drillfourholesof10mmdiameterequallyspaced
equal,equally
aroundtheboltcircle."
F
f Anitalicf(Latinsmallletterf)writtenonalinerepresentingasurfacewasanoldwayofindicatingthatthe
surfacewastobemachinedratherthanleftintheascastorasforgedstate.The"f"camefrom"finish"in
thesenseof"machinefinish"asopposedtorawstock/casting/forging.LatertheASAconvenedupona
finish
letterV(specificallyasansserifV)touchingthesurface.Soonthisevolvedintothe"checkmark"signwith
accompanyingnumberthattellsthereaderamaxroughnessvalue(RMS,microinchesormicrometres)
forthemachinedfinish,tobemeasuredwithaprofilometer.
FAO Anotetellingthemanufacturerthatallsurfacesofthepartaretobemachined(asopposedtoleavingany
surfacesascastorasforged).Notanobsoleteusage,butnotseenascommonlyasitwasdecadesago
notleastbecausepartsthatoncewouldhavebeenspotfacedcastingsarenowlikeliertobecontoured
frombilletwithCNCmilling.Butmoreimportantly,bestengineeringpracticetoday,reflectingdesignfor
manufacturabilityandavoidanceofspuriouscostdrivers,iseithertospecifyspecific,quantifiable
finishallover
requirementsforsurfaceswithspecificneeds(suchasRMSroughnessmeasurementsinmicroinchesor
micrometres,plusanyplatingorpaintingneeds),ortoleavefinishoutofthepartdefinition(andthusat
themanufacturer'sdiscretion)becauseitisnotimportanttofit,function,orcriticality.Thissamespiritis
behindtheshiftinmilitarystandardsfromwritingrequirementsaboutmethodstowritingtheminstead
aboutperformance,withthemethodtoreachthatgoalbeinguptotheingenuityofthedesigner.
FCF Therectangularbox(withseveralcells)thatconveysgeometrictolerancesinGD&T.Ittypicallytellsyou
whatsortofgeometriccondition(e.g.,parallel,perpendicular,round,concentric),followedbywhatsize

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featurecontrolframe (andmaybeshape)thetolerancezoneis,andfinallywhichdatumsitrelatesto,theorderofgagingagainst
them,andwhatmaterialconditionappliestothem(LMC,MMC,orRFS).Adiametersymbol()tellsyou
thatthezoneforthegeometrictoleranceiscylindrical.
FDorF/D The[main]fieldofthedrawing,asopposedtootherareasofit,suchasthepartslist(P/L),generalnotes
(G/N),flagnotes(F/NorFL),titleblock(T/B),revblock(R/B),billofmaterials(B/MorBoMorBOM),orlist
fieldofthedrawing ofmaterials(L/M).Rationalesfordrawingchangesthatarenotedintherevblockoftenusethese
abbreviationsforbrevity(e.g.,"DIM14.00was12.50addeddefaultTOLinfotoT/Baddedleaderlinesto
F/DaddedalternatehardwareIDstoP/LaddedalternatealloytoL/M").
FIM fullindicator
SeealsoTIR.
movement
FL Anotethatiscalledoutinspecificspotsinthefieldofthedrawing.Itisnumberedwithastylizedflag
flagnote,flagnote
symbolsurroundingthenumber.Ageneralnoteappliesgenerallyandisnotcalledoutwithflags.
FNorF/N 1.Flagnote:Aflagnoteisanotethatiscalledoutinspecificspotsinthefieldofthedrawing.Itis
numberedwithastylizedflagsymbolsurroundingthenumber(orsometimesadeltasymbol).Ageneral
flagnote,flagnotefind
noteappliesgenerallyandisnotcalledoutwithflags.2.Findnumber:"FN"meaning"findnumber"refers
number
totheordinalnumberthatgivesanIDtagtooneoftheconstituentsinapartslist(listofmaterials,billof
materials).Thus"fastenusingFN7"referstoafastenerthatis"findnumber"7inthelist.
FoS Atypeofphysicalfeatureonapart.AnFoSisafeaturethatcanhavesizeassociatedwithit,usually
involvingtheoppositionoftwosurfaces(e.g.,thetwodiametricallyoppositesidesofaholewallthetwo
oppositewallsofaslotorflange).Featuresofsize(FoSs)inrealityalwayshaveactualsizesandforms
featureofsize thatdifferfromtheirtheoreticalsizeandformthepurposeoftolerancingistodefinewhetherthe
differenceisacceptableornot.Thusmaterialcondition(LMC,MMC,somewhereinbetween,orRFS)is
importantinGD&T.)AgivengeometrictolerancemaybedefinedinrelationtoacertainFoSdatumbeing
atLMCoratMMC.
FS Thedrawingnotations"nearside"and"farside"tellthereaderwhichsideofthepartafeatureison,in
occasionalcontextswherethatfactisnotcommunicatedusingtherulesofprojectionalone.Contextsof
usageareratherlimited.Oneexampleisholelocations"3XAND3XFARSIDE"definessymmetrical
groupsof3holesonbothsidesofapart(6total),withouthavingtoredefineequivalentholecenter
coordinatesontwoseparateviews,oneforeachgroup.Thisisnotonlyaconvenienceforthedesigner
butalsoamethodoferrorprevention,becauseitprovidesawaytoavoidforkinggeometricdefinitionthat
farside
ideallyshouldbekeptunforkedtopreventdiscrepancies.Forexample,thegroupsdefinedabovecannot
accidentallybecomeasymmetricallydiscrepantinafuturerevisionbytherevisorfailingtoreviseboth
groupsequally(becausetheirdefinitionisunifiedinonlyoneplace).Anotherexampleispartmarking
locations.Anareaforpartidentificationmarkingcanbecircledonatopviewbutassignedtoeitherthetop
orbottomofthepartsimplywitha"nearside"or"farside"notationwhichobviatesaddinganyotherwise
unneededbottomviewtothefieldofthedrawing.
FSCM FederalStock/Supply
Codefor Anoldernamefor"CAGEcode".AlsoNSCM(NationalStock/SupplyCodeforManufacturers).
Manufacturers
G
GCI graycastiron
GD&Tor geometric
GDT dimensioningand Astandardizedlanguagefordefiningandcommunicatingdimensionsandtolerances.
tolerancing
GNorG/N generalnote(s) Mostengineeringdrawingshaveanoteslist,whichincludesbothgeneralnotesandflagnotes.
H
HBW hardness,Brinell, SeeBrinellscale.(The"W"comesfromtheelementsymbolfortungsten,W,whichcomesfromthe
tungstentip GermanWolfram.)
HHCS hexheadcapscrew
HRA hardness,Rockwell,A
SeeRockwellscale.
scale
HRB hardness,Rockwell,B
SeeRockwellscale.
scale
HRC hardness,Rockwell,C
SeeRockwellscale.
scale
HRS hotrolledsteel
HTTR heattreat,heat

treatment
H&TorH/T hardenedand
Aformofheattreatmentinwhichthemetalisfirsthardenedandthentempered.CompareN&T.
orHT tempered
I
AcommonneedinengineeringdrawingsistoinstructtheusertodoactivityXinaccordancewithtechnical
standardY.Forexample,"WeldallsubassembliesIAWAWSXYZ.123"means"Weldallsubassembliesin
accordancewithAmericanWeldingSocietystandardnumberXYZ.123"(thenumberishypotheticalinthis
example).Theword"per"isfunctionallyequivalentto"IAW"insuchcontextsthus"rivetallsheetmetal
IAW inaccordancewith perMILPRF123456"or"[...]IAWMILPRF123456".Partofthemotivationbehindthechoiceofwords"in
accordancewith"isthattheydonotallegethatanyparticularactivityisexplicitlyspecifiedbystandard
XYZ.123(which"per"couldbeinterpretedasalleging,atleastinconnotation)rather,thesewordsmerely
instructtheuserthatwhatevers/hedoesmustnotcontradictthestandardinanyway.Butthisisasubtle
connotativedistinction,and"per"and"IAW"aredenotativelyequivalent.
ID innerdiameter
identity,identification
number

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ISO International Andthemanystandardsthatitspecifies,forexample,ISO10303
Organizationfor
Standardization
J
K
KEY Drawingcalloutsmarked"KEY"define"keycharacteristics"thatareconsideredespeciallyimportantforfit,
key
function,safety,orotherreasons.Theyarethussubjectedtohigherinspectionsamplinglevels.
KPSI,kpsi kilopoundspersquare
inch,thatis,
SeediscussionatsynonymKSI.
thousandsofpounds
persquareinch
KSI,ksi kilopoundspersquare KSI(orksi),alsoabbreviatedKPSIorkpsi,isacommonnonSImeasurementscaleforultimatetensile
inch,thatis, strength,thatis,thenumberofunitsoftensileforcethatamaterialcanendureperunitofcrosssectional
thousandsofpounds areabeforebreaking.IntheSIsystem,theunitisthepascal(Pa)(oramultiplethereof,oftenmegapascals
persquareinch (MPa),usingthemegaprefix)or,equivalentlytopascals,newtonspersquaremetre(N/m).
L
LH Referringtohandedness,suchasthehelixhandednessofscrewthreadsorthemirrorimagehandedness
lefthand
ofasymmetricalpairofparts.
LMorL/M Alsocalledabillofmaterials(BoM,BOM).Overlapsalotinconceptwithapartslist(PLorP/L).Thereis
listofmaterials
noconsistentlyenforceddistinctionbetweenanL/M,aBoM,oraP/L.
LMC AmaterialconditioninGD&T.Meansthatafeatureofsize(FoS)isatthelimitofitssizetoleranceinthe
directionthatleavestheleastmaterialleftonthepart.Thusaninternalfeatureofsize(e.g.,ahole)atits
leastmaterial
biggestdiameter,oranexternalfeatureofsize(e.g.,aflange)atitssmallestthickness.TheGD&Tsymbol
condition
forLMCisacircledL.(SeealsoMMCandRFS.)Agivengeometrictolerancemaybedefinedinrelation
toacertainFoSdatumbeingatLMCoratMMC.
M
MACH machinemachined
MAJ major Asinmajordiameter,ormajorcharacteristic(forsamplinglevel)
MAX[2] maximum
MBD Definitionofthepartviaa3DCADmodelratherthanviaa2Dengineeringdrawing.Drawingsmaybe
modelbaseddefinition
printed(plotted)fromthemodelforreferenceuse,butthemodelremainsthegoverninglegalinstrument.
MBP measurement
threads,splines,gears(internal,female)(synonymouswithMBW)(seealsoMOP,MOW)
betweenpins
MBW measurement
threads,splines,gears(internal,female)(seealsoMBP,MOP,MOW)
betweenwires
MForM/F Whenonepartnumberismadefromanother,itmeanstotakepartAandmachinesomeadditional
makefrom
featuresintoit,creatingpartB.ThepartslistorL/M,inthe"material"field,willsay"M/FPN12345".
MFD manufactured
MFG manufacturing
MFR manufacturer MaybethesameentityastheCDAorODA,ormaynotbe.
MIL AprefixforthenamesofvariousUnitedStatesMilitaryStandardsandSpecifications,forexample,MIL
[U.S.]Military
STD*,MILSPEC*,MILDTL*,MILPRF*,MILA*,MILC*,MILS*,MILSTD1913,MILSTD1397.
MIN[2] minimumminutes

minor
MMC AmaterialconditioninGD&T.Meansthatafeatureofsize(FoS)isatthelimitofitssizetoleranceinthe
directionthatleavesthemostmaterialleftonthepart.Thusaninternalfeatureofsize(e.g.,ahole)atits
maximummaterial
smallestdiameter,oranexternalfeatureofsize(e.g.,aflange)atitsbiggestthickness.TheGD&Tsymbol
condition
forMMCisacircledM.(SeealsoLMCandRFS.)Agivengeometrictolerancemaybedefinedinrelation
toacertainFoSdatumbeingatLMCoratMMC.
MOD,MoD MinistryofDefence
SeealsoDOD.
[U.K.andothers]
MOP,MoP measurementover
threads,splines,gears(external,male)(synonymouswithMOW,measurementoverwires)
pins
MOW,MoW measurementover
threads,splines,gears(external,male)(seealsoMBW,MBP,MOP)
wires
MPa,MPA ThecommonSImeasurementscaleforultimatetensilestrength(UTS),thatis,thenumberofunitsof
tensileforcethatamaterialcanendureperunitofcrosssectionalareabeforebreaking.Thereisonlyone
correctcasingforthesymbol,capMcapPsmalla,which,likeanySIunitofmeasurementsymbol,
megapascals
properlyshouldbepreservedevenwhensurroundingtextisstyledinallcaps(whichlatterisafrequently
employedtraditioninengineeringdrawing).Butitisnotuncommontosee"MPA"throughcarelessness.
Usersarenotconfusedregardless.InnonSIterms,theunitforUTSistheKSI(orksi),whichseeherein.
MRB Acommitteethatreviewssomenonconformingmaterialswhicharesubmittedaspotentiallystill
materialreviewboard
usable/saleable(ifthenonconformancedoesnothinderfitorfunction).
MS StandardsestablishedbytheU.S.militaryandwidelyusedintheaerospacemanufacturing(militaryand
[U.S.]Military
civil)andotherdefenseindustries.StandardhardwaresometimesusestheMSprefixinthecatalog
Standard
numbers.(SeealsoANandNAS.)
N
NAS StandardsmaintainedbySAEInternationalandwidelyusedintheaerospacemanufacturingindustries.
NationalAerospace The"National"formerlyimplicitlyreferencedtheUSA,buttodayNASandotherstandardsareused
Standards globally.StandardhardwareforaerospaceworksometimesusestheNASprefixinthecatalognumbers.
(SeealsoANandMS.)

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NC National The[U.S.]NationalCoarseseriesofpre1949correspondstodaytotheUnifiedNationalCoarse(UNC)of
Coarsenumerical theUnifiedThreadStandard.
control
NCM nonconforming Thisabbreviationisusedinamachineshopwhenrecordingnonconformances(outoftolerance,etc.).For
material(s) example,"AnNCMtagwastiedtothescrappart."
NCR nonconformance Areportlistingnonconformances(outoftolerance,etc.).Helpstoanalyzesystemweaknesses(suchas
report wornoutequipment,operatorsinneedofmoretraining,orriskypractices).
NEC notelsewhere
Inthesenseof"notelsewhereclassified",theabbreviationiswellknownwithincertainfields,butnot
classifiedNational
otherstoavoidconfusion,spellout.TheNationalElectricalCodeisastandardforelectricalwork.
ElectricalCode
NEF The[U.S.]NationalExtraFineseriesofpre1949correspondstodaytotheUnifiedNationalExtraFine
NationalExtraFine
(UNEF)oftheUnifiedThreadStandard.
NF The[U.S.]NationalFineseriesofpre1949correspondstodaytotheUnifiedNationalFine(UNF)of
NationalFine
theUnifiedThreadStandard.
NLorN/L noteslist Alistofnotesthatappearssomewhereonthedrawing,oftenintheupperleftcorner.
NOM[2] nominal
NORMor
normalized referringtonormalization,astressrelievingheattreatment.SeealsoHTTR.
NORMD
NPS NavalPrimary
(Nottobeconfusedwithannotatingstraitpipe.ThisshouldbeabbreviatedNPSM,NPSLorNPSH[4])
Standard[3]
NPT NationalPipeTaper AsubsetseriesoftheUnifiedThreadStandard.
NS 1.NationalSpecial,ascrewthreadseriesseeUnifiedThreadStandard.Anextensibleseries,covering
NationalSpecialnear variousspecialthreads.2.Nearside:Thedrawingnotations"nearside"and"farside"tellthereader
side whichsideofthepartafeatureison,inoccasionalcontextswherethatfactisnotcommunicatedusingthe
rulesofprojectionalone.Contextsofusageareratherlimited.See"farside"forexamples.
NSCM NationalStock/Supply
Codefor Anoldernamefor"CAGEcode".AlsoFSCM(FederalStock/SupplyCodeforManufacturers).
Manufacturers
N&TorN/T normalizedand Aformofheattreatmentinwhichthemetalisfirstnormalized(stressrelieved)andthentempered.
orNT tempered CompareH&T.
NTS nottoscale SeealsoEngineeringdrawing>Scale.
O
OAL overalllength
OC oncenter(s) Thatis,centretocentredefinescentretocentredistanceoftwofeatures,suchastwoholes.
OD outerdiameter
ODA Theentitythatoriginallydesignedapart.ComparetoCDA,theentitythatcurrentlyhasdesignauthority
originaldesignactivity
overthepartdesign(definition).
OHL Thisabbreviationisusedinamachineshopwhenrecordingnonconformances.Forexample,"part
overhighlimit
scrappedbecauseIDisOHL."SeealsoULL.
OPP opposite SeePartnumber>Symmetricalpartsforexplanation.
ORIG original
P
pc,pcs piece,pieces
PD pitchdiameter
PDM,PDMS productdata
management,product
Adatabase(s)andrelatedapplication(s)thatfacilitateallaspectsofmanagingdatafilese.g.,TDPs,TDP
datamanager[app],
versions,drawings,modeldatasets,specs,addenda,certs,memoranda,EOs,ECOs,DCNs,RFQs,
productdata
quotes,POs,emails,faxes,photos,wordprocessordocuments,spreadsheets.SeealsoPLM.
managementsystem
[app]
PHorP/H precipitation
hardening,

precipitation
hardenedpilothole
PHRBRZ phosphorbronze
PLorP/L Alist,usuallytabularandoftenonthedrawing(ifnotaccompanyingthedrawingonaseparatesheet),
partslist listingthepartsneededinanassembly,includingsubparts,standardparts,andhardware.Thereisno
consistentlyenforceddistinctionbetweenanL/M,aBoM,oraP/L.
PLM productlifecycle
managementplant SeealsoPDM.
lifecyclemanagement
PNorP/N partnumber
POI Apointthatmakeseasierthelayout,toolpathprogramming,orinspectionofthepart.Itis
theintersectionpointoflinesthatmaynotmeetonthefinishedpart,suchasthetangentlinesof
pointofintersection
acurveorthetheoreticalsharpcorner(TSC)thatedgebreakinganddeburringwillremove.See
alsoSC,TSC,andAC.
PSI poundspersquare
Aunitofmeasurementforpressure.SeealsoKSI.
inch
PTFE polytetrafluoroethylene AlsowellknownbythebrandnameTeflon.
Q

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QMS qualitymanagement Asysteminplacetoensurethatqualityofmanufactureisproducedandmaintainedasystemtoprevent
system defectivepartsfrombeingmade,or,evenifmade,fromgettingintofinishedinventories.
QTYorqty quantity
R
R Radiusofanarcorcircle.Flatsandreversals(fallingwithinthedimensionaltolerancezone)aretolerated
radius
unless"CR"(controlledradius)isexplicitlyspecified.
RA,Ra roughness,
averageRockwellA SeesurfaceroughnessseeRockwellscale.
scale
RB,Rb RockwellBscale SeeRockwellscale.
RC,Rc RockwellCscale SeeRockwellscale.
REFor()[2] Thedimensionornoteisgivenonlyforreferenceandthusisnottobeusedasapartacceptancecriterion
(althoughitmaybeusedasanaidtoproductionorinspection).Thedimensionmayalsobesurrounded
byparenthesestosignifyareferencedimension.Whenadimensionisdefinedinoneviewbutalso
reference mentionedagaininanotherview,itwillbegivenasreferenceinthesecondcase.Thisrulepreventsthe
mistakeofdefiningitintwodifferentwaysaccidentallythe"main"(nonreference)mentionistheonlyone
thatcountsasafeaturedefinitionandthusasapartacceptancecriterion.Seealsobasicdimensions,
whicharesimilarinsomerespects.
REQDor Forexample,"4REQD"writtennexttoafastenermeansthatfourofthosefastenersarerequiredforthe
required
REQ'D assembly.
REV Engineeringdrawingsandmaterialorprocessspecificationsareoftenrevisedtheusualrevision
controlconventionistolabeltheversionsA,B,C,D,etc.arevisionblock(revblock)isatabularareaon
thedrawing(typicallyintheupperrightcorner)thatliststherevisionletters,abriefdescriptionofthe
changesandreasons,andapprovalinitialsanddates.Revisionsbeyond"Z"startthealphabetoveragain
withdoubling,e.g.,AA,AB,AC,AD,andsoon.Inthedaysofmanualdrafting,redrawingwasexpensive,
revision
soengineeringorders(EOs,ECOs,DCNs,ECNs)werenotalwaysincorporatedintoanextletterrevision.
TheythusaccompanythedrawingaspartoftheTDP.Withthedisseminationofsoftwareusage(CAD,
CAM,PDMSs),revisioncontrolisoftenbetterhandlednowadays,incompetenthandsatleast.Inrecent
yearstherevisioncontrolofengineeringdrawingshasevenbeenstandardizedbyASME,intheirstandard
Y14.35M.[5]
RFS regardlessoffeature Amaterialcondition(ormoreprecisely,freedomfromsuch)inGD&T.Meansthatagivengeometric
size toleranceistrueinrelationtoacertaindatumregardlessofitsactualsize(LMCactualsizeMMC).
RH Referringtohandedness,suchasthehelixhandednessofscrewthreadsorthemirrorimagehandedness
righthand
ofasymmetricalpairofparts.
RHR roughnessheight
Seesurfaceroughness.
reading
RMA returnmaterial
SeealsoRTV.
authorization
RMS RMSingeneralisastatisticaltechniquetodefinearepresentativevalueforagroupofdatapoints.With
regardtosurfaceroughness,itmeansthattheheightsoftheindividualmicroscopicpeaksandvalleys
rootmeansquare
shallbeaveragedtogetherviaRMStoyieldameasurementofroughness.Seealsohereinfasafinish
mark.
RTorR/T roughturn,rough Roughturnedmeansturnedonalathebutnotfinishedtoafinalmachineddimensionandsurface
turnedroom roughness.Canapplytobarstockortopartsinprocess.Roomtemperatureissometimesabbreviated
temperature "RT"withintablesofspecsforfinishingoperations(plating,painting,etc.).
RTP Theissuanceofadrawingfromtheengineering/designactivitytotheproductionactivity.Inotherwords,
releasetoproduction theeventwhenadraftbecomesacompleted,officialdocument.Astamponthedrawingsaying"ISSUED"
documentsthatRTPhasoccurred.
RTV roomtemperature
1.RTVsealants,awaytosealjoints.2.Returntovendor,sendpartsbacktoavendorforreworkor
vulcanizingreturnto
refundbecausetheyarenonconforming.SuchRTVoftenrequiresanRMA.
vendor
RZ,Rz roughness,mean
Seesurfaceroughness.
depth
S
SAE FormerlytheSociety
ofAutomotive
Andthemanystandardsthatitissues,forexample,theSAEAMSandSAEASstandardsseries.
EngineersnowSAE
International
SCorS/C Dimensionsmaybegivenas"acrosssharpcorners"althoughthecornersgetradiused.Inotherwords,
distancesmaybegivenfromintersectionpointswherelinesintersect,regardlessofedgebreaksorfillets.
sharpcorners
Thisisusuallyimpliedbydefault,so"S/C"oftenneednotbeexplicitlyadded.Butinsomecasesitclarifies
thedefinition.SeealsoTSC,POI,andAC.
SForS/F spotface
SFACEor
spotface
S/FACE
SHCS socketheadcapscrew Acapscrewwithasockethead(usuallyimplyingahexsocket,drivenwithahexkey.
SHN shown SeePartnumber>Symmetricalpartsforexplanation.
SHSS socketheadsetscrew Asetscrewwithasockethead(usuallyimplyingahexsocket,drivenwithahexkey.
SI Systmeinternational
[d'units][International Themetricsysteminitscurrentform(lateststandards).
SystemofUnits]
SNorS/N serialnumber

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SOLANN solutionanneal,
solutionannealed
SPECorspec specification
SPHERANN spheroidizeanneal
SPOTFACE Spotfacing
SR sphericalradius Radiusofasphereorsphericalsegment.
SSorS/S stainlesssteel 1.Stainlesssteel,seealsoCRES.2.Supersede/supersedes/superseded,referstowhenonedocument
supersede (specification,standard,drawing,etc.)replaces(supersedes)another(seealsorevisioncontrol).
SST Asomewhatunusualabbreviationspelloutforclarity."SS"or"CRES"aremorelikelytoberecognized
stainlesssteel
withcertainty.
STD Standard
STEP Standardfor
theExchange AstandardformatdefinedbyISO10303forMBDdatageneration,storage,andexchange.
ofProductModelData
STA solutiontreatedand

aged
STI screwthreadinsert
STL steel
STK stock Anominaldimensionforthestockmaterial,suchasbarstock
T
TAP Tappedhole Usuallyimpliesdrillingaholeiftheholedoesnotalreadyexist.
TBorT/B Anareaofthedrawing,almostalwaysatthebottomright,thatcontainsthetitleofthedrawingandother
keyinformation.Typicalfieldsinthetitleblockincludethedrawingtitle(usuallythepartname)drawing
number(usuallythepartnumber)namesand/orIDnumbersrelatingtowhodesignedand/or
manufacturesthepart(whichinvolvessomecomplicationbecausedesignandmanufacturingentitiesfora
givenpartnumberoftenchangeovertheyearsduetomergersandacquisitions,contract
letting,privatization,andthebuyingandsellingofintellectualpropertyseeCDAandODA)company
name(seepreviouscomment)initials/signaturesoftheoriginaldraftsman(aswellsastheoriginal
titleblock
checkerandtracerinthedaysofmanualdrafting)initials/signaturesofapprovingmanagers
(issuance/releasetoproductioninformation)crossreferencestootherdocumentsdefaulttolerancing
valuesfordimensions,geometry,andsurfaceroughnessrawmaterialinfo(ifnotgiveninaseparate
list/billofmaterials)andaccesscontrolinformation(informationaboutwhoisauthorizedtopossess,view,
orsharecopiesoftheinformationencodedbythedrawing,e.g.,classificationnotices,copyright
notices,patentnumbers).Drawingrevision(versioning)informationisnotalwaysincludedinthetitleblock
becauseitoftenappearsinaseparaterevisionsblock.
TDP Thecompletepackageofinformationthatdefinesapart,ofwhichthedrawingitselfisoftenonlyasubset.
technicaldata Italsoincludesengineeringorders(drawingchangenotices),3Dmodeldatasets,datatables,
package memoranda,andanyspecialconditionscalledoutbythepurchaseorderorthecompanies'termsand
conditionsdocuments.
THDorthd thread
THRU Optionallyappliedtoaholedimensiontosignifythattheholeextendsthroughtheworkpiece.For
Through example,THRUmaybestatedinaholedimensionifthehole'sendconditionisnotclearfromgraphical
representationoftheworkpiece.[6]
THRUALL SimilartoTHRU.Sometimesusedonholedimensionsforclaritytodenotethattheholeextendsthrough
Throughall
multipleopenspacefeaturesasitgoesthroughthewholeworkpiece.[7]
Ti titanium
TiN titaniumnitride[plating]
TIR totalindicatorreading
Formeasurementsofeccentricityandotherdeviationsfromnominalgeometry
totalindicatedrunout
TOL tolerance,tolerancing
TSC theoreticalsharp
SeediscussionatSCandPOI.
corner(s)
TY type Foranexplanationof"type"abbreviatedas"TY",seetheexamplegivenat"CL"meaning"class".
TYP[2] Otherfeaturessharethesamecharacteristic.Forexample,ifthedrawingshows8holesonaboltcircle,
andjustoneisdimensioned,with"TYP"or"(TYP)"followingthedimensionlabel,itmeansthatthatholeis
typicalofall8holesinotherwords,itmeansthattheother7holesarethatsizealso.Thelatestrevisions
Typical ofY14.5deprecate"TYP"byitselfinfavorofthespecifyingofanumberoftimes,suchas"2X"or"8X".
Thishelpsavoidanyambiguityoruncertainty.TYPorTypicalwasdescribeinMilStd8,thedirectingbody
priortoadoptionofthedimensiontoleranceinterpretationY14.5series.ItslastrevisionwasCin1963,but
canstillbefoundinmanyolderaircraftdrawings.
U
UAI useasis OneofthepossibleMRBdispositions.Othersincludescrapandrework.
ULL Thisabbreviationisusedinamachineshopwhenrecordingnonconformances.Forexample,"part
underlowlimit
scrappedbecauseODisULL."SeealsoOHL.
UNC UnifiedNational
AsubsetseriesoftheUnifiedThreadStandard.
Coarse
UNEF UnifiedNationalExtra
AsubsetseriesoftheUnifiedThreadStandard.
Fine
UNF UnifiedNationalFine AsubsetseriesoftheUnifiedThreadStandard.
UNJC UnifiedNational"J" AsubsetseriesoftheUnifiedThreadStandard,withcontrolledrootradiusandincreasedminordiameter.
seriesCoarse Forapplicationsrequiringmaximumfatigueresistanceamidchronicvibration(suchasinaircraft).

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UNJF UnifiedNational"J" AsubsetseriesoftheUnifiedThreadStandard,withcontrolledrootradiusandincreasedminordiameter.
seriesFine Forapplicationsrequiringmaximumfatigueresistanceamidchronicvibration(suchasinaircraft).
UNS UnifiedNational UnifiedNationalSpecialisasubsetseriesoftheUnifiedThreadStandard.Itisanextensibleseries,
Specialunified coveringvariousspecialthreads.Theunifiednumberingsystemisavaguelynamedstandardfor
numberingsystem namingalloysbyprincipalelementpercentages.
UON unlessotherwise
Alittleused(thusnotwellrecognized)abbreviation.Toavoidconfusion,spellout.
noted
UOS unlessotherwise
Afairlywellknownabbreviation,buttoavoidconfusion,spellout.
specified
USASI UnitedStatesof
AmericaStandards FormernameforANSI(19661969).
Institute
USS U.S.StandardthreadsbecametheNationalseries(e.g.,NC,NF,NEF),whichbecametheUnifiedNational
UnitedStates
series(e.g.,UNC,UNF,UNEF)seeUnifiedThreadStandard.AsforU.S.Steel,itwasoncethelargest
StandardUnited
steelcompanyonearth,oftenanapprovedsupplier,andnotinfrequentlyasolesourcehenceitsmention
StatesSteel
ondrawings.
UTS ultimatetensile
strengthUnified
ThreadStandard
V
v Aletterv(Latinsmallletterv)writtenonalinerepresentingasurfaceisawaytoindicatethatthesurface
istobemachinedratherthanleftintheascastorasforgedstate.Theoldersymbolforthiswasasmall
script(italic)f(seehereinf).LatertheASAconveneduponaletterV(specificallyasansserifV)touching
finish
thesurface.Soonthisevolvedintothe"checkmark"signwithaccompanyingnumberthattellsthereader
amaxroughnessvalue(RMS,microinchesormicrometres)forthemachinedfinish,tobemeasuredwith
aprofilometer.
W
WC tungstencarbide The"W"comesfromtheelementsymbolfortungsten,W,whichcomesfromtheGermanWolfram.
WI Boththematerialandtheabbreviationareobsolete,ornearlyso.Spelloutthewordsifthismaterialisto
wroughtiron
bementionedatallinmoderndrawings.
W/I,w/i within Alittleusedabbreviation.Bettertospelloutforclarity.
W/O,w/o without Bettertospelloutforclarity.
X
_X_ usedtoindicatethe WhentheletterXisprecededbyaspace,thismeans"by".Forexample,achamfermaybecalledoutas
wordby 12X45
X[2]or() Whenadimensionisusedinmultipleplaceseitheroftheseprefixescanbeaddedtothedimensionto
definehowmanytimesthisdimensionisused.Thisexamplesignifieseightplaces.Thereshouldbeno
numberofplacesfor whitespacebetweenthenumeralandtheletterX.(Noteoncharacterencoding:Althoughintypography
example,8Xor(8) (includingUnicode)theletterXandthemultiplicationsign()aredistinctcharacterswithdifferingglyphs,it
isalongstandingtraditioninengineeringdrawingthattheletterXisinterchangeablewiththemultisign,
unlessotherwisespecifiedbytheCAxsystemsused.)
Y
Y14.X Callsoutthedrawingstandardthatthisdrawingisfollowing.Forexample,ASMEY14.5andY14.100are

commonlyusedstandardsthatdefineallofthesymbolsanddraftingconventionsused.
YS yieldstrength
Z

<<<EngineeringDrawing>>>

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