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.

 

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 0.236 25.4 0.189 0.007 24 0.413 5.1 9 6.2
1 0.209 28.2 0.167 0.006 21 0.365 4.5 16 5.5
2 0.185 31.4 0.147 0.006 19 0.324 4.0 22 4.9
3 0.161 34.8 0.127 0.005 17 0.282 3.4 29 4.2
4 0.142 38.5 0.111 0.005 16 0.248 3.0 31 3.7
5 0.126 43.0 0.098 0.004 14 0.220 2.7 37 3.3
6 0.110 47.9 0.085 0.004 13 0.193 2.3 42 2.9
7 0.098 52.9 0.075 0.003 11 0.172 2.1 46 2.6
8 0.087 59.1 0.066 0.003 10 0.152 1.8 50 2.3
9 0.075 65.1 0.057 0.003 9 0.131 1.6 1/16 2.0
10 0.067 72.6 0.050 0.003 8 0.117 1.4 54 1.8
11 0.059 82.0 0.044 0.002 7 NULL 1.2 56 1.6
12 0.051 90.7 0.038 0.002 7 NULL 1.1 60 1.4
13 0.047 99.9 0.035 0.002 6 NULL 1.0 62 1.2
14 0.039 99.9 0.028 0.002 6 NULL 0.8 1/32 1.0
15 0.035 99.9 0.025 0.002 5 NULL 0.7 70 0.9
16 0.031 99.9 0.022 0.001 5 NULL 0.6 73 0.8