British Association Threads

A British system of threads with 47.5° included angle with rounded roots and crest. Even numbers are the preferred sizes.

Title
B.A.Tapping DrillClearance Drill
 inchesmminchesmm
00.1894.80.2426.147
10.1664.2160.2135.410
20.1473.7340.1914.851
30.12853.2640.1664.216
40.1112.8190.1473.734
50.0982.4890.1363.454
60.0862.1840.1162.946
70.0761.9300.1042.462
80.0671.7020.09352.375
90.05951.5110.0812.057
100.04651.1810.0731.854
110.0421.0670.0671.702
120.0370.9400.0551.397
130.0350.8890.0551.397
140.0280.7110.04691.191
150.0250.6350.0401.016
160.02250.572  
170.0200.508  
180.0180.457  
190.01450.368  

Reference

BS 93:1951 - Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A.

BS 93:2008 - British Association (B.A.) screw threads. Requirements

See also: Acme Thread, British Standard Whitworth, Metric Threads, Thread, UNC, UNF.

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Subjects: Fixings and Fasteners