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 08/30173466 DC

Publication history

First published May 1919
Second edition, May 1951
Third edition, September 2008

Foreword

Publishing information

This British Standard is published by BSI and came into effect on 30 September 2008. 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This British Standard supersedes BS 93:1951, which is withdrawn.

Relationship with other publications

This British Standard is intended for use with BS 919‑2, which specifies the corresponding screw gauges.

Information about this document

This British Standard has been fully revised to bring it up to date. This British Standard specifies the British Association (B.A.) system of screw threads, which comprises 17 graded metric sizes designated by the numbers 0 to 16. Approximate inch equivalents are also given.

Hazard warnings

WARNING — Attention is drawn to the fact that, with the different screw thread forms available, there is the possibility of a 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.

Presentational conventions

The provisions of this standard are presented in roman (i.e. upright) type. Its requirements are expressed in sentences in which the principal auxiliary verb is “shall”.

Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element.

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 British Standard specifies limits of sizes, and tolerances, for single start parallel screw threads of British Association (B.A.) form. It is not applicable to screw threads associated with interference fits, such as those on the “metal ends” of studs and in the corresponding tapped holes.

This British Standard specifies the following:

basic sizes for B.A. threads, sizes 0 B.A. to 16 B.A.;
limits of size, and tolerances, for close class and normal class external threads of sizes 0 B.A. to 10 B.A.;
limits of size, and tolerances, for normal class external threads of sizes 11 B.A. to 16 B.A.;
limits of size, and tolerances, for a single class of internal threads of sizes 0 B.A. to 16 B.A.

2 Normative references

3 Terms and definitions and symbols

4 Profile of British Association (B.A.) screw thread

5 Basic sizes of B.A. threads

6 Tolerance classes and limits of sizes, and tolerances, for B.A. threads

7 Gauges

Bibliography

BS 93:2008

British Association (B.A.) screw threads. Requirements

Current

Published:

30 Sep 2008