B.A. Screw Threads
(British Association)


The revised specification for B.A. screw threads, B.S. 93, recommends that the B.A. system be used in preference to the B.S.W. and B.S.F. for all screws smaller than ¼ in., but that the 0 B.A. thread be discontinued in favour of the ¼ in. B.S.F. Preference should be given to even numbered B.A. sizes. 
 © Tom Martin 2001

 
©Tom
 Martin 2001
No.		 Dimensions in mm. Approximate dimensions in In. Approximate
threads
per inch
Diameter Pitch Diameter Pitch
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25 		 6.00
5.00
4.70
4.10
3.60
3.20
2.80
2.50
2.20
1.90
1.70
1.50
1.30
1.20
1.00
0.90
0.79
0.70
0.62
0.54
0.48
0.42
0.37
0.33
0.29
0.25 		 1.00
0.90
0.81
0.73
0.66
0.59
0.53
0.48
0.43
0.39
0.35
0.31
0.28
0.25
0.23
0.21
0.19
0.17
0.15
0.14
0.12
0.11
0.10
0.09
0.08
0.07 		 0.2362
0.2087
0.1850
0.1614
0.1417
0.1260
0.1102
0.0984
0.0866
0.0748
0.0669
0.0591
0.0512
0.0472
0.0394
0.0354
0.0311
0.0276
0.0244
0.0213
0.0189
0.0165
0.0146
0.0130
0.0114
0.0098 		 003937
003543
003189
002874
002598
002322
002087
001890
001693
001536
001378
001220
001102
000984
000906
000827
000748
000669
000591
000551
000472
000433
000394
000354
000315
000276 		 25.4
28.2
31.4
34.8
38.5
43.1
47.9
52.9
59.1
65.1
72.6
82.0
90.7
102.00
110.00
121.00
134.00
149.00
169.00
181.00
212.00
231.00
254.00
282.00
318.00
363.00 
Index