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 07/30158483 DC

Publication history

First published as BS 84:1918 and BS 92:1919
Second edition as BS 84 (incorporating BS 92) May 1940
Third edition, September 1956
Fourth edition, November 2007

Foreword

Publishing information

This British Standard 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This British Standard supersedes BS 84:1956, which is withdrawn.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 includes tables of basic sizes, limits and tolerances for British Standard Whitworth (B.S.W.) and British Standard Fine (B.S.F.) screw threads. In addition it provides a “Selected thread” series of recommended diameter/pitch combinations for use in applications where the standard coarse (B.S.W.) and fine (B.S.F.) series have insufficiently fine pitches.

An allowance (minimum clearance) is provided on certain classes of external threads of sizes up to and including 34 in diameter; the recommended combinations of classes of internal threads and external threads include internal threads having larger effective diameter tolerances than the corresponding sizes of external threads. Three tolerance classes are specified for external threads, close, medium and free. The allowance is provided for medium class and free class external threads by specifying maximum external thread limits below the basic size. The purpose of this allowance is to provide for the threads to be coated if necessary, the coating encroaching within the allowance; it is also intended to permit easy assembly of maximum material condition (MMC) external threads and internal threads, thus facilitating the use of torque wrenches. Two tolerance classes of internal threads are specified, medium and normal.

Close class internal threads are now non-preferred but, in view of their usage in the past and for special uses, limits and tolerances for these are specified in Annex E.

No change has been made in the general three-part formula used as a basis for tolerancing effective diameters, and the formulae used for tolerancing the other thread elements also remain unchanged from those in BS 84:1956; the reason for this is to minimize any changes in the sizes of the gauges used to control the size of the finished work.

The table of recommended diameter/pitch combinations for screw threads in the “Selected thread” series follows very closely the corresponding table (Table 37) in BS 1580‑1.

The foreword of BS 84:1956 ended with the following statement. “In conclusion it may be asked why the revision of this standard has been undertaken in view of the standardization of the Unified thread in BS 1580. The reason is that Whitworth threads will undoubtedly continue to be used for many years, especially on replacements or spare parts.” The present revision of BS 84 has been undertaken because, fifty years on, this continues to be the case.

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 Whitworth form, for general engineering use. It is not applicable to threads for threaded pipe joints, screw threads associated with interference fits, such as those on the “metal ends” of studs and in the corresponding tapped holes, or to screw threads which are to be subjected to high temperatures.

This standard specifies the following thread series:

a coarse thread series, the British Standard Whitworth (B.S.W.) series, with nominal diameters in the range 18 in to 6 in.
a fine thread series, the British Standard fine (B.S.F.) series, with nominal diameters in the range 316 in to 414 in.
NOTE The tables of limits and tolerances for the B.S.F. series extend up to the 3 in size only, since nominal sizes above 3 in are rarely used.
a supplementary selected thread (WHIT. S.) series with nominal diameters from 14 in to 7 in.
a truncated Whitworth form series (specified in Annex A).

This British Standard specifies limits of sizes, and tolerances, of uncoated threads and also for metal coated threads (including threads coated with nickel, tin or zinc) with a thickness of coating of the order of 0.000 2 in. It is not applicable to heavily coated threads (i.e. threads with a coating thickness above 0.000 35 in).

NOTE Supplementary information is given in Annex B, Annex C and Annex D.

2 Normative references

3 Terms and definitions and symbols

3.1 Terms and definitions

3.2 Symbols

4 Profile of Whitworth screw thread

5 Tolerance classes of external and internal threads

6 Limits of sizes, and tolerances, for uncoated B.S.W. and B.S.F. threads

7 Limits of size, and tolerances, for B.S.W. and B.S.F. coated threads

8 Stainless steel external threads

9 Selected thread series

9.1 General

9.2 Basic sizes

9.3 Design sizes

9.4 Tolerances

10 Designation of screw threads of Whitworth form

11 Gauges

Bibliography

BS 84:2007

Parallel screw threads of Whitworth form. Requirements

Current

Published:

30 Nov 2007