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BSP Threads

Tuesday, 11th May 2021
Graham (Tech Advisor)

BSP Threads are used for most Oxygen, Acetylene and Propane equipment.

Fuel Gases, Acetylene, Propane, Polypropylene etc will have Left Hand Threads because this stops Fuel Gas and Non Fuel Gas equipment from being mixed up, which is potentially VERY dangerous.

Left Hand Threads will have small cuts machined into the Nut to indicate they are Left hand.

Fuel Gas has Left Hand Thread

Non Fuel Gases Oxygen, Argon, Argon/Co2 Mix etc, will have Right Hand Threads and so no cut on the Nut.

BSP Thread Sizes

The size of BSP Threads causes a lot of confusion because, for example, a 3/8″BSP Thread is over 1/2″ in diameter!

BSP stands for “British Standard Pipe” and is a very old thread.

In the example of 3/8″BSP, 3/8″ is the diameter of the BORE of the pipe NOT the outside diameter of the thread.

If the BORE of the pipe is 3/8″ diameter, clearly the outside diameter of the pipe has to be greater and it’s this outside pipe diameter that a thread would be cut into. So the Thread diameter has to be greater than the 3/8″ BORE diameter of the pipe!

BSP Thread Diameters

Gas equipment typically uses 4 different BSP Threads, the following is the basic specifications of these threads.

SizeOutside DiameterPitch
1/8″0.383″ (9.73mm)28 TPI
1/4″0.518″ (13.16mm)19 TPI
3/8″0.656″ (16.66mm)19 TPI
5/8″0.902″ (22.91mm)14 TPI

BSP Thread Uses in Gas Equipment

1/8″BSP is commonly used for the outlet thread on small Regulators, the type used for throwaway cylinders for example.

1/4″BSP is typically used on the Torch end of Oxygen, Acetylene & Propane Hoses where small torches, including Lightweight and Model ‘O’, are used.

3/8″BSP is typically used for Regulator Outlets, Flash Arrestor Inlet + Outlet and the Torch end of Hoses where larger Torches, including Heavy Duty and Cutting Torches, are used.

5/8″BSP is typically used for Gas Cylinder Outlet and therefore Regulator Inlet.

I hope you found this article useful.

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  1. Simon says:

    Thanks Graham, this cleared up some confusion about whether a new argon regulator was the right size. These BSP size designations are a pain to deal with if ypu’re not used to them!

    1. Graham says:

      Hi Simon, thanks for the comment. BSP threads are a constant source of confusion 🙂 I wrote the article after I had a customer get quite aggressive on the phone. I told him his thread was 3/8″BSP, but he INSISTED it was 5/8″ because he had measured it. It took a while to explain, he then thought it was a stupid way to measure a thread, like it was my fault! 🙂
      Cheers Graham

  2. Adekunle says:

    Thanks graham for the timing info. More Grace

    1. Graham says:

      You’re welcome, glad you found the info useful.
      Cheers Graham

  3. Peter Smith says:

    Excellent info,Graham, helps judge size immediately. Thank you for your informative blogs.

    1. Graham says:

      Hi Peter
      Thank you for your comment, much appreciated, and you’re very welcome, I’m glad you found the information useful.
      Best Regards

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