British Association Threads

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

Favoured by model engineers, Stuart Turner models are traditionally supplied with odd numbered BA nuts and Bolts.

BA Threads
B.A. # Tapping Drill Clearance Drill
  inches mm inches mm
0 0.189 4.8 0.242 6.147
1 0.166 4.216 0.213 5.410
2 0.147 3.734 0.191 4.851
3 0.1285 3.264 0.166 4.216
4 0.111 2.819 0.147 3.734
5 0.098 2.489 0.136 3.454
6 0.086 2.184 0.116 2.946
7 0.076 1.930 0.104 2.462
8 0.067 1.702 0.0935 2.375
9 0.0595 1.511 0.081 2.057
10 0.0465 1.181 0.073 1.854
11 0.042 1.067 0.067 1.702
12 0.037 0.940 0.055 1.397
13 0.035 0.889 0.055 1.397
14 0.028 0.711 0.0469 1.191
15 0.025 0.635 0.040 1.016
16 0.0225 0.572
17 0.020 0.508
18 0.018 0.457
19 0.0145 0.368
  • 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

 

About Nigel 117 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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