Publishing and copyright information

The BSI copyright notice displayed in this document indicates when the document was last issued.

The following BSI references relate to the work on this standard:
Committee reference FME/9
Draft for comment 07/30158486 DC

Publication history

First published June 1963
Second edition, March 1981
Third edition, November 2007

Foreword

Publishing information

This part of BS 3643 is published by BSI and came into effect on 30 November 2007. It was prepared by Subcommittee SFTSE/1, Screws and fasteners technical specification committee, under the authority of Technical Committee FME/9, Nuts, bolts and accessories. A list of organizations represented on this committee can be obtained on request to its secretary.

Supersession

This part of BS 3643 supersedes BS 3643‑1:1981, which is withdrawn.

Information about this document

The start and finish of text introduced or altered by Corrigendum No. 1 is indicated in the text by tags .

Relationship with other publications

This part of BS 3643 is based on a series of BS ISO, and ISO, standards for ISO metric general purpose screw threads, each clause, from Clause 4 onwards, being based on one BS ISO, or ISO, as follows:

Clause 4: Basic profile: BS ISO 68‑1:1998;
Clause 5: General plan: BS ISO 261:1998;
Clause 6: Basic dimensions: ISO 724:1993;
Clause 7: Tolerances – Principles and basic data: BS ISO 965‑1:1998;
Clause 8: Tolerances – Deviations for constructional screw threads: BS ISO 965‑3:1998;
Clause 9: Tolerances − Limits of sizes for hot-dip galvanized external screw threads to mate with internal screw threads tapped with tolerance position H or G after galvanizing: BS ISO 965‑4:1998;
Clause 10: Tolerances – Limits of sizes for hot-dip galvanized external screw threads to mate with internal screw threads with maximum size of tolerance position h before galvanizing: BS ISO 965‑5:1998.

BS 3643 consists of the following parts:

Part 1: Principles and basic data;
Part 2: Specification for selected limits of size.

BS 3643‑2 specifies the fundamental deviations, tolerances and limits of size for the tolerances classes 4H, 5H, 6H and 7H for internal threads and 4h, 6g and 8g for external threads where appropriate for:

a course pitch series with the range 1 mm to 68 mm diameter;
a fine pitch series with the range 1 mm to 33 mm diameter;
a constant pitch series with the range 8 mm to 300 mm diameter.

Information about this document

This part of BS 3643 has been revised to bring it up to date. The 1981 edition of the standard was based on ISO 68:1963, ISO 261:1973, ISO 724:1968, ISO 965‑1:1980 and ISO 965‑3:1980. These standards have all been withdrawn and superseded and this part of BS 3643 has been revised to reflect the latest editions of these standards (see above).

Two extra clauses have been added to this revision, based on BS ISO 965‑4:1998 and BS ISO 965‑5:1998, respectively.

This part of BS 3643 does not include a clause based on BS ISO 965‑2:1998. Selected limits of size for use in the UK are specified in BS 3643‑2:2007.

This part of BS 3643 also does not include a clause based on BS ISO 262:1998 as these sizes can be expected to be specified in the relevant product standards. However, the data given in BS ISO 262:1998 have been included in Table 3.

Additional guidance notes are given in Annex A. These notes are presented separately so as not to disrupt the correspondence between the clauses of the main text and the BS ISO, or ISO, standards on which they are based. Information is given in Annex B on calculating limits of size for metric screw threads for which dimensions are not given in the tables in this part of BS 3643. This information is given because it is recognized that the limitations placed by the BS ISO and ISO standards on nominal sizes and on the diameter/pitch combinations, might in certain cases need to be exceeded.

Hazard warnings

WARNING — Attention is drawn to the fact that, with the different screw thread forms available, there is the possibility of mismatch, which is potentially hazardous. It is the responsibility of the designer of the end product to ensure that this possibility is reduced to a minimum. For further information on mismatches of screw thread systems see PD 6494.

Contractual and legal considerations

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

1 Scope

This part of BS 3643 gives a compilation of principles and basic data for single-start, parallel screw threads having the ISO basic profile for triangular screw threads. Guidance on calculating limits of size for metric screw threads not included in Tables 1 to 14 is given in Annex B.

2 Normative references

3 Terms and definitions and symbols

3.1 Terms and definitions

3.2 Symbols

4 Basic profile

4.1 General

4.2 Dimensions

5 General plan

5.1 General

5.2 Designation

5.3 Choice of diameter and pitch

6 Basic dimensions

6.1 General

6.2 Basic dimensions

7 Tolerances — Principles and basic data

7.1 General

7.2 Structure of the tolerance system

7.3 Designation

7.4 Tolerance grades

7.5 Tolerance positions

7.6 Lengths of thread engagement

7.7 Crest diameter tolerances

7.8 Pitch diameter tolerances

7.9 Root contours

7.10 Recommended tolerance classes

7.11 Formulae

8 Tolerances — Deviations for constructional threads

8.1 General

8.2 Deviations

9 Tolerances — Limits of sizes for hot-dip galvanized external screw threads to mate with internal screw threads tapped with tolerance position H or G after galvanizing

9.1 General

9.2 Designation

9.3 Deviations

9.4 Limits of sizes — External screw threads — Coarse thread series

10 Tolerances — 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

10.1 General

10.2 Designation

10.3 Deviations

10.4 Limits of sizes — Internal screw threads — Coarse thread series

Bibliography

BS 3643-1:2007

ISO metric screw threads - Principles and basic data

Current

Published:

30 Nov 2007