BS 93 – British Association (B.A.) screw threads. Requirements

BS 93:2008 specifies limits of sizes, and tolerances, for single start parallel screw threads of British Association (B.A.) form. The 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.

BS 93 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.

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.

BS 93 is intended for use with BS 919-2:2007, which specifies the corresponding screw gauges.

This British Standard has been fully revised to bring it up to date. BS 93:2008 supersedes BS 93:1951, which is withdrawn.