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British Standard Pipe (BSP) use Whitworth threads and are identifiable by its parallel thread and 60 degree internal cone on the male fittings. There is also a tapered variant (BSPT).

BSP Thread ID

To identify a male thread, measure the outer diameter, as in the picture and compare with the tables below.
To identify a female thread, measure the internal diameter, as in the picture, and compare with the tables below.
Thread Id
Dimension given in the following tables are not exact measurements and are given as a means of comparing and identifying threads. All adaptors are made to engineering tolerances and there will be variations in dimensions because of this.
Dash SizeThread SizeThreads Per InchFemale Parallel Thread I.D (mm)Male Parallel Thread O.D. (mm)
-201 1/4″1138.942.1
-241 1/2″1145.247.6

BSP Pressure Ratings and Torque Values

Thread size Type G Class ADashsizeISO 8434-6 + NCB 174Swepts
Working Pressure with O-ringWorking Pressure without O-ringTightening TorqueNot Applicable to push in adaptors
MpabarpsiMpabarpsiWith ‘O’ ring NmWithout ‘O’ ring NmMpabarpsi
1 1/4″-20202002900161602175190210191902755
1 1/2″-2416160232012.5125181224029017.51752540

DESIGN DETAILS AND SPECIFICATIONS SUBJECT TO CHANGE WITHOUT PRIOR NOTICE – Whilst every effort has been made to ensure the accuracy of the information supplied herein, Burnett & Hillman cannot be held responsible for any errors or omissions (E&OE). Working pressures quoted are taken from the relevant standard and are provided as a guide only.