ISO

INTERNATIONAL STANDARD 6157-1

First edition
1988-08-01

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION

ORGANISATION INTERNATIONALE DE NORMALISATION
MEXAYHAPOAHAfl OPTAHM3A~MR l-l0 CTAH~APTM3A~MM

Fasteners - Surface discontinuities -

Part 1:
Bolts, screws and studs for general requirements
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L%men ts de fixation -
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Defau ts de surface -

Partie 7: Boulons, vis et goujons d usage g&Gral

ISO 6157-1:1988
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3e8672f193c3/iso-6157-1-1988

Reference number
ISO6157-1 :1988 EI

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bodies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch member
body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all
matters of electrotechnical standardization.

Draft International Standards adopted by the technical committees are circulated to

the member bodies for approval before their acceptance as International Standards by
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the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.

International Standard
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ISO 6157-1 was prepared by Technical Committee ISO/TC 2,
Fasteners.
ISO 6157-1:1988
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Users should note that all International Standards undergo revision from time to time
3e8672f193c3/iso-6157-1-1988
and that any reference made herein to any other International Standard implies its
latest edition, unless othetwise stated.

0 International Organkation for Standardkation, 1988

Printed in Switzerland
INTERNATIONAL STANDARD ISO 6157-1 : 1988 (E)

Fasteners - Surface discontinuities -

Part 1:
Bolts, screws and studs for general requirements

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(standards.iteh.ai)
1 Scope and field of application NOTES
ISO 6157-1:1988 1 The figures in clause 3 are examples only. They apply correspond-
ingly also to other types of bolts, screws and studs.
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1.1 This part of ISO 6157 establishes limits for various types
3e8672f193c3/iso-6157-1-1988
of surface discontinuities on bolts, screws and studs for general 2 The individual figures show the surface discontinuities exaggerated
requirements. in some cases for clarity.

lt applies to bolts, screws and studs with

2 References
- nominal thread diameters 5 mm and larger; ISO 468, Sutface roughness - Parameters, their values and
general rules for specifying requiremen ts.
- product grades A and B;
ISO 898-1, Mechanical properties of fasteners - Part 1: Bolts,
- property classes up to and including 10.9, unless other- screws and studs.
wise specified in product Standards or agreed between
supplier and purchaser. ISO 2859, Sampling procedures and tables for inspection by
a ttribu tes.

1.2 Limits for surface discontinuities on bolts, screws and ISO 3269, Fasteners - Acceptance inspection.
studs for special requirements (e.g. automatic assembly) are
laid down in ISO 6157-3. When the engineering requirements
of the application necessitate that sur-face discontinuities on 3 Types, Causes, appearance and limits
bolts, screws and studs be more closely controlled, it should be of surface discontinuities
specified in the respective product Standard, or the purchaser
shall specify the applicable limits in the inquiry and purchase 3.1 Cracks
Order.
A Crack is a clean (crystalline) fracture passing through or
across the grain boundaries and may possibly follow inclusions
1.3 Where the permissible limits for surface discontinuities of foreign elements. Cracks are normally caused by overstress-
indicated in clause 3 occur, the minimum values for the ing the metal during forging or other forming operations, or
mechanical and functional properties specified in ISO 898-1 during heat treatment. Where Parts are subjected to significant
should still be met. reheating, Cracks usually are discoloured by scale.
ISO6157-1:1988(E)

3.1.1 Quench Cracks

Cause Quench Cracks may occur during hardening due to excessively high thermal and transformation Stresses. Quench
Cracks usually follow an irregular and erratic course on the sut-face of the fastener.
Appearance Quench Crack across top
of head. Usually an
Quench Crack circum- extension of Crack in
Quench Crack
shank or side of head
at corner of head uench Crack at root

K Longitudinal quench Crack

Quench Crack across washer face

and to depth of washer face thickness

Quench Crack extending

radially into fillet

A-A
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‘Quench Crack’
at root

Limits Quench Cracks of any depth, any length, or in any location are not permitted.

3.1.2 Forging Cracks

Cause Forging Cracks may occur during the tut-off or forging operations and are located on the top of the head of
screws and bolts and on the raised periphery of indented head bolts and screws.
Appearance

Forging Crack on top of head

Limits Length, 1, of forging Cracks : 1 < dl)

Depth or width, b, of forging Cracks: b 6 0,04d

1) d= nominal thread diameter

 ISO 6157-1 : 1988 (EI

3.1.3 Forging bursts

Cause Forging bursts may occur for example during forging on the flats or corners of the heads of bolts and screws, at
the periphery of flanged or circular head products or on the raised periphery of indented head bolts and screws.
Appearance
Forging burst

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Limits Hexagon head screws
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No forging burst in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head
surface (chamfer circle) or into the underhead bearing surface. Forging bursts occurring at the intersection of
ISO 6157-1:1988
two wrenching flats shall not reduce the width across corners below the specified minimum.
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Forging bursts in the raised 3e8672f193c3/iso-6157-1-1988
periphery of indented head bolts and screws shall not exceed a width of 0,06dl) or
have a depth extending below the indented Portion.

Circular head screws

Flanges of bolts and screws and peripheries of circular head screws may have forging bursts, but they shall not
exceed the following limits :
Width of forging bursts:

0,08d,*) (with only one forging hurst);

0,04d, (with two or more forging bursts, one of which may extend to 0,08d,L

1) d= nominal thread diameter

2) d,= head or flange diameter

ISO6157=1:1988(E)

3.1.4 Shekr bursts

Cause Shear bursts may occur, for example during forging, frequently at the periphery of products having circular or
flanged heads, and are located at approximately 45’ to the product axis.

Shear bursts may also occur on the sides of hexagon head products.
Appearance
S hear bursts

* Shear bursts

Limits Hexagon iTeh STANDARD PREVIEW

head screws

(standards.iteh.ai)
No shear burst in the flats of hexagon bolts and screws shall extend into the crown circle on the top of the head
surface (chamfer circle) or into the underhead bearing surface. Shear bursts, occurring at the intersection of two
wrenching flats, shall not reduce the width across corners below the specified minimum.
ISO 6157-1:1988
Shear bursts inhttps://standards.iteh.ai/catalog/standards/sist/3c110000-825e-4706-a9b5-
the raised peripher-y of indented head bolts and screws shall not exceed a width of 0,06dl) or have
a depth extending below the indented Portion.
3e8672f193c3/iso-6157-1-1988
Circular head screws

Flanges of bolts and screws and peripheries of circular head products may have shear bursts, but shall not exceed
the following limits :

Width of shear bursts:

0,08@ (for only one shear burst);
0,04d, (with two or more forging shear bursts, one of which may extend to 0,08d,).

1) d= nominal thread diameter

2) d, = head or flange diameter

4
 ISO6157-1 : 1988 EI

3.2 Raw material seams and laps

A seam or lap is a narrow, generally straight or smooth curved line discontinuity running longitudinally on the thread, shank or head.

Cause Seams and laps are inherent in the raw material from which fasteners are made.
Appearance
Lap or seam, usually straight or
smooth curved line discontinuity

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Limits Permissible depth : 0,03d 1)

lf laps or seams extend into the head, they shall not exceed the permissible limits for width and depth specified
for bursts (sec 3.1.3).

1) d= nominal thread diameter

ISO 61574 : 1988 (EI

3.3 Voids

A void is a shallow pocket or hollow on the surface of a bolt or screw due to non-filling of metal during forging or upsetting.

Cause Voids are produced by marks and impressions due to Chips (shear burrs) or by tust formation on the raw material.
They are not eliminated during forging or upsetting operations.
Appearance

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Limits Depth, h, of voids:
ISO 6157-1:1988
h < 0,02 dl) https://standards.iteh.ai/catalog/standards/sist/3c110000-825e-4706-a9b5-
: 0,25 mm max.
3e8672f193c3/iso-6157-1-1988
Area of all voids:

The combined surface area of all voids on the bearing face shall not exceed ?O 96 of the total area.

1) d= nominal thread diameter

6
 ISO61574 : 1988 (EI

3.4 Folds
A fold is a doubling over of metal which occurs at the surface of the fastener during forging.

Cause Folds are produced by material displacements due to lack of congruence of forms and volumes of the Single
forging Steps.
Appearance

Permissible,
typical “clever/
leaf” fold -J’
in non-circular
shoulder fastener

Permissible, at the intersection

between flange and driving part

Permissible, at

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bolt end
of the

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Permissible, fold
at exterior corner
ISO 6157-1:1988
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3e8672f193c3/iso-6157-1-1988

Limits Folds at interior corners at or below the bearing surface are not permissible, unless specifically permitted in this
patt of ISO 6157 or in the product Standard.

Folds at exterior corners are permissible.

3.5 Tool marks

Tool marks are longitudinal or circumferential grooves of shallow depth.

Cause Tool marks are produced by the movement of manufacturing tools over the surface of the bolt or screw.
Appearance
Tool mark
7

Permissible tool mark

from trimming Operation

Limits Tool marks produced by machining in the shank, fillet or bearing sutface shall not exceed a surface roughness of
I REJ= 3,2 pm when tested in accordance with ISO 468.