INTERNATIONAL ISO

STANDARD 965-1

Third edition
1998-12-15

ISO general purpose metric screw

threads — Tolerances —
Part 1:
Principles and basic data
Filetages métriques ISO pour usages généraux — Tolérances —
Partie 1: Principes et données fondamentales
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A Reference number
ISO 965-1:1998(E)
 ISO 965-1:1998(E)

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. Each 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, governmental 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 voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

International Standard ISO 965-1 was prepared by Technical Committee ISO/TC 1, Screw threads, Subcommittee
SC 2, Tolerances.

This third edition cancels and replaces the second edition (ISO 965-1:1980), which has been technically revised.

ISO 965 consists of the following parts, under the general title ISO general purpose metric screw threads —
Tolerances

— Part 1: Principles and basic data

— Part 2: Limits of sizes for general purpose bolt and nut threads – Medium quality

— Part 3: Deviations for constructional screw threads

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— Part 4: Limits of sizes for hot-dip galvanized external threads to mate with internal threads tapped with
tolerance position H or G after galvanizing

— Part 5: Limits of sizes for internal screw threads to mate with hot-dip galvanized external screw threads with
maximum size of tolerance position h before galvanizing
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© ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland

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 INTERNATIONAL STANDARD © ISO ISO 965-1:1998(E)

ISO general purpose metric screw threads — Tolerances —

Part 1:
Principles and basic data

1 Scope
This part of ISO 965 specifies the basic profile for ISO general purpose metric screw threads (M) conforming to
ISO 261.

The tolerance system refers to the basic profile in accordance with ISO 68-1.

2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of
ISO 965. At the time of publication the editions indicated were valid. All standards are subject to revision, and
parties to agreements based on this part of ISO 965 are encouraged to investigate the possibility of applying the
most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid
International Standards.

ISO 68-1:1998, ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads.
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ISO 261:1998, ISO general purpose metric screw threads — General plan.

ISO 262:1998, ISO general purpose metric screw threads — Selected sizes for screws, bolts and nuts.

ISO 724:1993, ISO general purpose metric screw threads — Basic dimensions.

ISO 898-1:—1), Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws
and studs.

ISO 965-2:1998, ISO general purpose metric screw threads — Tolerances — Part 2: Limits of sizes for general
purpose bolt and nut threads — Medium quality.

ISO 965-3:1998, ISO general purpose metric screw threads — Tolerances — Part 3: Deviations for constructional
screw threads.

ISO 1502:1996, ISO general purpose metric screw threads — Gauges and gauging.
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ISO 5408:1983, Cylindrical screw threads — Vocabulary.

1) To be published. (Revision of ISO 898-1:1988)

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 ISO 965-1:1998(E) © ISO

3 Definitions and symbols

3.1 Definitions

For the purpose of this part of ISO 965 the definitions given in ISO 5408 apply.

3.2 Symbols

The following symbols are used:

Symbol Explanation

D basic major diameter of internal thread

D1 basic minor diameter of internal thread

D2 basic pitch diameter of internal thread

d basic major diameter of external thread

d1 basic minor diameter of external thread

d2 basic pitch diameter of external thread

d3 minor diameter of external thread

P pitch

Ph lead

H height of fundamental triangle

S designation for thread engagement group "short"

N designation for thread engagement group "normal"

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L designation for thread engagement group "long"

T tolerance

TD1, TD2
tolerances for D1, D2, d, d2
Td1, Td 2

ei, EI lower deviations (see figure 1)

es, ES upper deviations (see figure 1)

R root radius of external thread

C root truncation of external thread

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 © ISO ISO 965-1:1998(E)

Figure 1 — Position of tolerances with respect to zero line (basic size)

4 Structure of the tolerance system

The system gives tolerances defined by tolerance grades and tolerance positions and a selection of grades and
positions.

The system provides for:

a) a series of tolerance grades for each of the four screw thread diameters, as follows:

Tolerance grades

D1 4, 5, 6, 7, 8

d 4, 6, 8

D2 4, 5, 6, 7, 8
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d2 3, 4, 5, 6, 7, 8, 9

Details of tolerance grades and combinations of tolerance grades for pitch and crest diameters according to tolerance quality
and length of engagement group required, with order of preference, are shown in clause 12.

b) Series of tolerance positions:

— G and H for internal threads;

— e, f, g and h for external threads.

The established tolerance positions comply with the need of current coating thickness and with the demands of easy
assembly.

c) Selection of recommended combinations of grades and positions (tolerance classes) giving the commonly used
tolerance qualities fine, medium and coarse for the three groups of length of thread engagement short, normal
and long. Moreover a further selection of tolerance classes is given for commercial bolt and nut threads.
Tolerance classes other than those shown in clause 12 are not recommended and shall only be used for
special cases.
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 ISO 965-1:1998(E) © ISO

5 Designation
5.1 General

The complete designation for a screw thread comprises a designation for the thread system and size, a designation for
the thread tolerance class followed by further individual items if necessary.

5.2 Designation of single-start screw threads

A screw thread complying with the requirements of the International Standards for ISO general purpose metric screw
threads according to ISO 68-1, ISO 261, ISO 262, ISO 724, ISO 965-2 and ISO 965-3 shall be designated by the letter
M followed by the value of the nominal diameter and of the pitch, expressed in millimetres and separated by the
sign "3".

EXAMPLE: M8 3 1,25

For coarse pitch threads listed in ISO 261, the pitch may be omitted.

EXAMPLE: M8

The tolerances class designation comprises a class designation for the pitch diameter tolerance followed by a class
designation for the crest diameter tolerance.

Each class designation consists of

 a figure indicating the tolerance grade;

 a letter indicating the tolerance position, capital for internal threads, small for external threads.

If the two class designations for the pitch diameter and crest diameter (major or minor diameter for internal and external
threads respectively) are the same it is not necessary to repeat the symbols.

EXAMPLES:
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 © ISO ISO 965-1:1998(E)

A fit between threaded parts is indicated by the internal thread tolerance class followed by the external thread tolerance
class separated by a stroke.

EXAMPLE:

M6 – 6H/6g

M20 ¥ 2 – 6H/5g6g

The absence of tolerance class designation means that tolerance quality "medium" with the following tolerance classes
are specified:

Internal threads

 5H for threads up to and including M1,4;

 6H for threads M1,6 and larger.

NOTE Except for threads with pitch P = 0,2 mm for which the tolerance grade 4 is defined only (see tables 3 and 5).

External threads

 6h for threads up to and including M1,4;

 6g for threads M1,6 and larger.

The designation for the group of length of thread engagement "short" S and "long" L should be added to the tolerance
class designation separated by a dash.

EXAMPLE: M20 3 2 – 5H – S

M6 – 7H/7g6g – L

The absence of the designation for the group of length of thread engagement means the group "normal" N is specified.

5.3 Designation of multiple-start screw threads

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Multiple-start metric screw threads shall be designated by the letter M followed by the value of the nominal diameter,
the sign 3, the letters Ph and the value of the lead, the letter P and the value of the pitch (axial distance between two
neighbouring flanks in the same direction) a dash, and the tolerance class. Nominal diameter, lead and pitch are
expressed in millimetres.

EXAMPLE: M16 3 Ph3P1,5 – 6H

Ph
For extra clarity the number of starts i.e. the value of may be added in verbal form and in paranthesis.
P

EXAMPLE: M16 3 Ph3P1,5 (two starts) – 6H

5.4 Designation of the left hand threads

When left hand threads are specified the letters LH shall be added to the thread designation, separated by a dash.

EXAMPLES: M8 3 1 – LH
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M6 3 0,75 – 5h6h – S – LH

M14 3 Ph6P2 – 7H – L – LH

M14 3 Ph6P2 (three starts) – 7H – L – LH