BA (British Association) Threads used widely in model engineering and electrical fasteners amongs others. The BA thread has an unusual thread angle of 47.5deg and threading inserts difficult to obtain. Most BA threads are cut using taps and dies.

 

Actions Ba No Outside Dia Inch Tpi Core Dia Inch Radius Thread Depth Thou Hex Across Flats Tapping Drill Size Mm Letter Or Number Drill Clearence Drill Mm
0 0.24 25.4 0.19 0.01 24 0.41 5.1 9 6.2
1 0.21 28.2 0.17 0.01 21 0.37 4.5 16 5.5
2 0.19 31.4 0.15 0.01 19 0.32 4.0 22 4.9
3 0.16 34.8 0.13 0.01 17 0.28 3.4 29 4.2
4 0.14 38.5 0.11 0.00 16 0.25 3.0 31 3.7
5 0.13 43.0 0.10 0.00 14 0.22 2.7 37 3.3
6 0.11 47.9 0.08 0.00 13 0.19 2.3 42 2.9
7 0.10 52.9 0.08 0.00 11 0.17 2.1 46 2.6
8 0.09 59.1 0.07 0.00 10 0.15 1.8 50 2.3
9 0.07 65.1 0.06 0.00 9 0.13 1.6 1/16 2.0
10 0.07 72.6 0.05 0.00 8 0.12 1.4 54 1.8
11 0.06 82.0 0.04 0.00 7 - 1.2 56 1.6
12 0.05 90.7 0.04 0.00 7 - 1.1 60 1.4
13 0.05 99.9 0.04 0.00 6 - 1.0 62 1.2
14 0.04 99.9 0.03 0.00 6 - 0.8 1/32 1.0
15 0.04 99.9 0.03 0.00 5 - 0.7 70 0.9
16 0.03 99.9 0.02 0.00 5 - 0.6 73 0.8