BSP (British Standard Pipe) Thread Data

Nominal
Size
(inches)

T
P
I

Pitch
(inches)

Major
Diameter
(inches)

Minor
Diameter
(inches)

Tapping
Drill
Size
1/16 28 0.0357 0.304 0.2583 Letter
Drill G
(6.6 mm)
1/8 28 0.0357 0.383 0.3372 11/32 in.
(8.73 mm)
1/4 19 0.0526 0.518 0.4546 11.8 mm
(0.4646 in)
3/8 19 0.0526 0.656 0.5886 15.25 mm
(0.6004 in.)
1/2 14 0.0714 0.825 0.7336 3/4 in.
(19.05 mm)
5/8 14 0.0714 0.902 0.8186 21 mm
(0.8268 in.)
3/4 14 0.0714 1.041 0.9496 24.5 mm
(0.9646 in.)
7/8 14 0.0714 1.189 1.0976 1.1122 in.
1 11 0.0909 1.309 1.1926 30.75 mm
(1.2106 in.)

This chart courtesy of British Tool Company.


BSP (British Standard Pipe) Thread Profile


Calculations

r = basic radius = 0.137329p
h = basic depth of thread = 0.640327p
p = pitch = 1/t.p.i.
Angle of thread = 55 degrees