What is BSPP thread?

What is BSPP Threads

The British Standard Pipe Parallel (BSPP) is a thread used to connect pipes and fittings. It’s a parallel thread, meaning that the sides of the thread are straight, as opposed to tapered like BSPT threads. This makes it easier to assemble and disassemble, but it also means that it’s not as good at sealing fluids under pressure. The BSPP male has straight threads and a 30˚ seat. The female port has straight threads and a spot-face as usual, or the BSPP male thread can also mate with a BSPOR (paralleled) female with a straight thread, a 30˚ seat, and an O-ring.

The Size of BSPP Thread

drawing BSPP

Inch size Dash size Thread Size Male Thread O.D. (in) Female thread O.D (in)
Inch size Dash size Thread Size Male Thread O.D. (in) Female thread O.D (in)
18 -2 18– 28 38 0.38 1132 0.35
14 -4 14– 19 3364 0.52 1532 0.47
38 -6 38– 19 2132 0.65 1932 0.60
12 -8 12– 14 1316 0.82 34 0.75
58 -10 58– 14 78 0.88 1316 0.80
34 -12 34– 14 1132 1.04 3132 0.97
1 -16 1 – 11 1516 1.30 1732 1.22
114 -20 114– 11 12132 1.65 1916 1.56
112 -24 112– 11 178 1.88 12532 1.79
2 -32 2 – 11 21132 2.35 214 2.26

Key Features:

  • Parallel threads: Unlike tapered threads like NPT, BSPP threads are straight, simplifying assembly and eliminating the need for thread sealant in most cases.
  • Measured in inches: Similar to NPT, BSPP thread sizes are designated in inches.
  • Sealing: BSPP threads rely on elastomeric seals (O-rings, bonded washers) or metal-to-metal sealing to create a leakproof connection. They don’t create a seal through thread interference like tapered threads.
  • Designation: Threads are designated by the letter “G” followed by the nominal size in inches (e.g., G 1/4, G 1/2).
  • Wide range of sizes: Available in various sizes from 1/8″ to 4″ and larger, catering to diverse piping needs.
  • High-pressure capability: Can handle moderate to high pressures depending on the material and application.
  • limited Interchangeable with BSPT: While distinct from the tapered BSPT threads, BSPP fittings can sometimes be interchangeable with certain BSPT counterparts using adapters.


  • Plumbing systems: Primarily used for connecting pipes and fittings in domestic and commercial plumbing systems.
  • Hydraulic systems: Commonly found in low- to medium-pressure hydraulic applications, particularly in countries following British standards.
  • Pneumatic systems: Used in compressed air systems in some settings.
  • Industrial equipment: Employed in various industrial machines and equipment where leak-proof pipe connections are needed.


  • Ease of assembly: Straight threads facilitate simple installation and maintenance, saving time and effort.
  • Leak-proof seal: Provides a reliable seal in most applications, reducing leak risks and minimizing maintenance needs.
  • Wide availability: Readily available in various sizes and types due to its established presence in the plumbing and hydraulic industries.
  • No thread sealant required: The sealing method eliminates the need for messy thread sealants, making them cleaner and less prone to leaks.
  • Interchangeability: Potential for interchangeability with BSPT in certain situations offers additional flexibility.


BSPP threads offer a convenient and reliable solution for connecting pipes and fittings in plumbing and low- to medium-pressure hydraulic systems in regions where they are the norm. Their ease of use, leak-proof performance, and widespread availability make them a popular choice for various applications.While capable of handling high pressures, may not be suitable for extremely high-pressure applications compared to dedicated high-pressure thread standards.


  • ISO 228-1: This international standard specifies the dimensions and tolerances for BSPP threads.
  • ISO 1179-1: This standard covers dimensions for threaded ports (female threads) used in hydraulic fittings and valves, based on BSPP threads.


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