Co-operating organizations

The Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations:

The Government department and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard:

This British Standard, having been approved by the Mechanical Engineering Industry Standards Committee, was published under the authority of the Executive Board on 22 February, 1972

The following BSI reference relates to the work on this standard: Committee references MEE/4

Foreword

In order to keep abreast of progress in the industries concerned, British Standards are subject to periodical review. Suggestions for improvements will be recorded and in due course brought to the notice of the committees charged with the revision of the standards to which they refer.

A complete list of British Standards, numbering over 9 000, fully indexed and with a note of the contents of each, will be found in the BSI Catalogue which may be purchased from BSI Sales Department. The Catalogue may be consulted in many public libraries and similar institutions.

This standard makes reference to the following British Standards:

BS 46, Keys and keyways and taper pins. Part 1. Keys and keyways.

BS 970, Wrought steels in the form of blooms, billets, bars and forgings. Part 1. Carbon and carbon manganese steels, including free cutting steels.

BS 4500, ISO limits and fits.

BS 4500‑1, General, tolerances and deviations.

This British Standard is the first of a series for metric keys and keyways and has been prepared under the authority of the Mechanical Engineering Industry Standards Committee.

The essential data for this standard have been extracted from ISO Recommendations R 773 ¹⁾ and R 774 ²⁾.

Although similar in principle to BS 46‑1, for inch keys and keyways, it provides for three classes of fit for square and rectangular parallel keys and keyways, namely, “free”, “normal” and “close”, and the provision of these three types of fit is in accordance with ISO practice.

In addition to the three classes of fit agreed by ISO as mentioned above, the United Kingdom has found it necessary to introduce an additional class, an interference fit. This is considered necessary to avoid the possibility of the rotation of the key which might occur in high torque, in reversing conditions, in applications where torsional vibration exists, or in precision applications.

The marked difference in dimensions between the inch and metric keys and keyways was, in the early days of metrication, the subject of considerable discussion and, quite naturally, fears were expressed that there would be problems due to the loading on the side faces of the key and keyway for any given shaft size.

These metric sections of keys have been in satisfactory use in most European countries for many years. It was, however, still desirable that there should be the satisfaction of more positive assurance that no design limitation exists in the application of the thinner metric key sections. At the request of technical committee MEE/4, the National Engineering Laboratory explored some of the questions which had been raised. The results of these investigations have been published and they demonstrate the effects of both static and dynamic tests, and include comparisons of the stresses and deformations of the two key forms at very high loadings. For the benefit of designers who are concerned with high static or dynamic torque loadings in keyed shafting systems, the reports are:

NOTE The titles of the British Standards referred to in this standard are listed on page 2.

The above reports are obtainable from the Reports Unit, National Engineering Laboratory, East Kilbride, Glasgow, to which enquirers should apply direct.’

A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 18 and a back cover.

This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

1 Scope

This British Standard relates to the following types of keys and keyways with dimensions in millimetres:

square parallel,
rectangular parallel,
square taper, gib-head and plain,
rectangular taper, gib-head and plain.

In addition, a fourth class of fit is provided in this British Standard to give an interference fit.

Three classes of fit are provided for the square and rectangular parallel keys and keyways, namely “free”, “normal” and “close”, and the dimensions and tolerances specified are in accordance with ISO Recommendations R 773³⁾ and R 774⁴⁾.

2 Fits

3 Material

4 Dimensions and tolerances

4.1

4.2

4.3

4.4

BS 4235-1:1972

Specification for metric keys and keyways - Parallel and taper keys

Current

Published:

22 Feb 1972