British Standard Brass Threads
26 TPI for all sizes.


Tube 
Size
Depth of
thread.
Double depth thread Root 
Diameter
Tapping
drill size
1/8
1/4
3/8
1/2
5/8
3/4
7/8
1
1-1/8
1-1/4
1-1/2 
.0246
.0246
.0246
.0246
.0246
.0246
.0246
.0246
.0246
.0246
.0246 
.0493
.0493
.0493
.0493
.0493
.0493
.0493
.0493
.0493
.0493
.0493 
.0757
.2007
.3257
.4507
.5657
.7007
.8257
.9507
1.0757
1.2007
1.4507 
47
6
Q
29/64
37/64
45/64
53/64
61/64
1-5/64
1-13/64
1-29/64 
000000000000000All dimensions are in inches© Tom Martin 2001
Index