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BSPP and BSPT Fittings

BSPP and BSPT are the British Standard Pipe threads, parallel and tapered, used on equipment from Europe and Asia. This sheet covers how they are designated, how each one seals and how to tell them from NPT.

Ref HY-0017ISO 228-1ISO 7-1ISO 1179

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Both threads use the 55° Whitworth thread form. BSPP (British Standard Pipe Parallel) is a straight thread defined in ISO 228-1 and designated G. A parallel thread does not seal on the thread, so BSPP joints seal with a bonded washer, an O-ring, an elastomer seal or a 60° cone seat. Hydraulic stud ends for BSPP ports are covered in ISO 1179. BSPT (British Standard Pipe Taper) is defined in ISO 7-1. It has a 1 in 16 taper and seals on the thread with sealant, like NPT. The thread pitch and diameter for each size are on the BSP thread chart.

How to identify

Check whether the male is tapered or parallel with a straightedge.
Measure the OD and the pitch. BSP uses Whitworth pitches, which differ from NPT in most sizes.
Use a 55° thread gauge. NPT is 60°; the difference shows as a poor gauge fit at the flanks.
On BSPP, look for a sealing face, an O-ring groove or a 60° cone in the female.

Designation decoder

Marking	Meaning	Seals by
G (ISO 228-1)	Parallel thread, male or female	A separate seal, O-ring or cone
R (ISO 7-1)	Taper male thread	Thread interference with sealant
Rp (ISO 7-1)	Parallel female for use with R male	Thread with sealant
Rc (ISO 7-1)	Taper female thread	Thread interference with sealant
BSPP, 60° cone	Female swivel seats on a male 60° cone	Metal-to-metal on the cone
ISO 1179 stud end with bonded washer	Bonded seal on the spot face	Washer rubber lip
ISO 1179 stud end with O-ring	O-ring in a groove under the hex	O-ring on the spot face
ISO 1179 metal-to-metal stud end	Sealing edge cuts into the spot face	Metal contact

Key points

BSPP and NPT share 14 TPI in 1/2 and 3/4 sizes but have different thread angles and diameters. They do not seal together.
BSPT and BSPP males can thread into each other's females part way. Do not rely on that joint.
Bonded washers are single use in most service guidance. Replace them at every reassembly.
Never use thread sealant on a BSPP joint that seals on a washer, O-ring or cone.
Assembly torque comes from ISO 1179 or the fitting maker.

Common mistakes

Calling every British fitting "BSP" without saying parallel or taper.
Using a JIC or NPT adapter on a BSPP port because it threads in.
Reusing flattened bonded washers.
Taping a BSPP 60° cone fitting.

Governing standards: ISO 228-1 (pipe threads where pressure-tight joints are not made on the threads); ISO 7-1 (pipe threads where pressure-tight joints are made on the threads); ISO 1179 (connections for BSPP ports). See the BSP thread chart.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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