British Thread Chart
British Thread Chart - Threads Per Inch.
Size
Cycle Engineers
Institute
(C.E.I.)Unified
Fine
(UNF)Unified
Coarse
(UNC)British
Standard
Fine
(BSF)British
Standard
Whitworth
(Coarse)
(BSW)
1/4"
26
28
20
26
20
5/16"
26
24
18
22
18
3/8"
26
24
16
20
16
7/16"
26
20
14
18
14
1/2"
20
20
13
16
12
9/16"
20
18
12
16
12
5/8"
20
18
11
14
11