National foreword

This British Standard is the UK implementation of ISO 2903:2016. Together with BS ISO 2901:2016, BS ISO 2902:2016, BS ISO 2904:2020 and BS ISO 965‑1:2013, it supersedes BS 5346:1976, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee FME/9, Fasteners.

A list of organizations represented on this committee can be obtained on request to its committee manager.

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.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 September 2016.

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.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.

The committee responsible for this document is ISO/TC 1, Screw threads.

This third edition cancels and replaces the second edition (ISO 2903:1993), Clauses 1, 13 and 14, and Table 7 of which have been technically revised (now Clauses 1, 11 and 12, and Table 5).

1 Scope

This document specifies a tolerance system for metric trapezoidal screw threads in accordance with ISO 2902. The tolerances refer to the design profile in accordance with ISO 2901.

The tolerance system does not apply to trapezoidal screw threads with special requirements on axial displacement, for example, machine tool lead and feed screws and nuts.

2 Normative references

3 Terms and definitions

4 Symbols

5 Tolerance system

6 Tolerance positions

7 Tolerance grades

8 Length groups of thread engagement

9 Recommended tolerance classes

10 Multiple-start threads

11 Formulae

11.1 General

11.2 Fundamental deviations

11.3 Crest diameter tolerances

11.4 Pitch diameter tolerances

11.5 Tolerances for minor diameter of external thread (T_d3)

11.6 Length groups of thread engagement

12 Designation

12.1 General

12.2 Designation of single-start threads

12.3 Designation of multiple-start screw threads

12.4 Designation of left-hand threads

Bibliography

BS ISO 2903:2016

ISO metric trapezoidal screw threads. Tolerances

Current

Published:

31 Oct 2020