BSP thread - everything you need to know

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What is the BSP thread?

The BSP thread is a type of pipe thread whose coils take the shape of a letter 'V' with an angle of 55 degrees. In addition, they have rounded ridges.

BSP threads are also referred to as British or Whitworth threads (named after the inventor of this standard)

Moreover, as the BSP thread standard originated in the UK, it uses the inch system of measurement.

BSP Thread Scheme

What are the types of BSP threads?

There are two types of BSP threads:

  • BSPP thread - Whitworth pipe thread, cylindrical. It is characterized by the fact that both the male and female parts are cylindrical. Requires additional sealing; 
  • BSPT thread - Whitworth pipe thread, tapered. Distinguished by the fact that the male part is tapered, and the female part is tapered or cylindrical. It is a self-sealing thread, so it does not need additional sealing.

What are the applications for the BSP thread?

BSP thread is used in a variety of industries, including power hydraulics and pneumatics. In addition, it is also widely used in low-pressure and water joints.

The BSP inch thread is one of the most common threads used throughout the world (except perhaps in the United States and Canada, where the US standard predominates).

What is the difference between NPT and BSP threads?

The main difference between the NPT threads and the BSP threads is in the coil angle of the threads - the NPT thread has a 60-degree coil angle and the BSP thread has a 55-degree coil angle.

Comparision of NPT Thread and BSP Thread

BSP means 'British Standard Pipe', which is the British standard. Whereas NPT means 'National Pipe Thread', which is the American standard.

The NPT thread has a slightly larger coil angle (60 degrees). In addition, the peaks are flattened rather than rounded as in BSP. The difference in angle makes the two standards slightly different in thread pitch.

In theory, you will screw an NPT into a BSP and vice versa, but the joint will have backlash that would need to be sealed.

What are the dimensions of BSP thread? BSP Thread Chart

In the chart below, you will find the dimensions that the BSP pipe thread is characterized by. However, the threads in practice may deviate minimally from these, which you should take into account when adjusting the correct size.

Thread size [inch] Number of coils per inch Thread pitch in [mm] Outer Diameter [mm] Inner Diameter [mm] Measuring Length in [mm]
1/8 28 0.907 9.728 8.565 3.97
1/4 19 1.337 13.157 11.445 6.012
3/8 19 1.337 16.662 14.95 6.35
1/2 14 1.814 20.955 18.633 8.164
3/4 14 1.814 26.441 24.12 9.525
1 11 2.309 33.249 30.292 10.391
1 1/4 11 2.309 41.91 38.953 12.7
1 1/2 11 2.309 47.803 44.846 12.7
2 11 2.309 59.614 56.657 15.875
2 1/2 11 2.309 75.184 72.227 17.463
3 11 2.309 87.884 84.927 20.638
4 11 2.309 113.03 110.073   
Female BSP Thread and Male BSP Thread

How to measure a BSP thread?

You can measure BSP threads using a calliper.

As for the outside diameter, catch the thread with the main jaws of the tool at its widest point (so that they rest on the coil) and read the result. In contrast, use the smaller jaws of the calliper to measure the inside diameter. Insert them into the thread hole, open them to the maximum, and read the result.

Measuring the thread pitch is a bit more complicated. Here, rest the large jaws of the calliper parallel to the edge of the thread so that they rest on top of two separate coils. Then check the result and divide it by the number of furrows (not humps!) that are between one jaw and the other.

Now compare the data you get with the chart. In this way, you will know which BSP inch threads you need.

Photo of Bartosz Kułakowski - CEO of Hosetech sp. z o. o.

Articles author

Bartosz Kułakowski

CEO of Hosetech Sp. z o.o.

Bartosz Kulakowski is an industrial hoses and couplings specialist with over 10 years of experience. Bartosz has been present in the technical industry since 2013. He gained experience as a technical and commercial advisor in the sector of plastic conveyor belts, steel structures, industrial hoses, and connectors. Since 2016, he has specialized exclusively in hoses and connectors. In 2019 he opened his own business under the HOSETECH Bartosz Kulakowski brand and since July 2022 he has been the CEO of the capital company HOSETECH Sp z o. o. (LLC).


What is the BSP thread?

What are the types of BSP threads?

What are the applications for the BSP thread?

What is the difference between NPT and BSP threads?

What are the dimensions of BSP thread? BSP Thread Chart

How to measure a BSP thread?