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British Standard Pipe (BSP) threads are by far the most popular with the United Kingdom, all of Europe, Australia, New Zealand, and South Africa adopting these standards.

Huiqi BSP thread fittings
Huiqi BSP thread fittings

What are BSPT and BSPP?

There are 2 types of threads: BSPT (British Standard Pipe Thread) and BSPP (British Standard Parallel Pipe). They both have a thread angle of 55°, BSPT is a tapered thread, whereas BSPP is a straight or parallel thread. This distinction plays a significant role in their application and sealing mechanisms.

90° Elbow BSPT Female 7T9
90° Elbow BSPT Female 7T9

BSPT Threads

BSPT (British Standard Pipe Thread) shares similarities with the NPT threads, but a significant difference is in the profile angle. The BSPT thread’s profile angle is 55° compared to NPT’s 60°. Despite this resemblance, NPT and BSPT threads cannot provide an efficient seal when connected together.

This thread is common in countries like Japan, China, and Britain. It’s also adopted in certain international standards like ISO7-1.

  • Thread conforms to ISO 228-1
  • Port conforms to ISO 1179
  • Pitch & diameter measured in inches e.g. G1/4-19
  • Parallel threads require o-ring, crush washer, gasket or metal to metal seal between connections for pressure tight connection
  • Thread angle is 55°

BSPP Threads

BSPP (British Standard Parallel Pipe) threads, also known as straight threads or G threads, have a consistent diameter and a tooth angle of 55°. The thread form does not naturally provide a seal, necessitating additional sealing materials.

BSPP threads are common in plumbing industries globally, particularly in regions such as the United Kingdom, Europe, Asia, Australia, New Zealand, and South Africa.

  • Thread conforms to ISO 7
  • Pitch and diameter are measured in inches, e.g. R3/8-19
  • Tapered thread profile seals by metal to metal interference fit, usually requires sealing compound for pressure tight connection
  • Taper angle is 1° 47′, the same as NPT(F)
  • Thread angle is 55°
  • Not interchangeable with NPT(F)

How are they different?

BSPT, similar to NPT, creates a seal by extrusion force when the male thread is screwed into the female thread. On the other hand, BSPP threads need an additional sealing material like an O-ring or a gasket to create a seal.

G Threads and Rp Threads

G and Rp threads are both 55° pipe threads. The coding differs depending on the country. For instance, China, France, the former Soviet Union, and Japan use the G code, while ISO uses the Rp code. British codes are BSP and BSPP, and German codes include R and K.

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