NPT and BSP are pipe thread standards used for screw threads on pipes and pipe fittings, used to seal pipes.

So, what’s the difference between them?

The difference has a lot to do with your location more so than the construction or application of the threads themselves. However, they’re not interchangeable due to some differences in the designs.

BSP used in UK, Europe, Asia, Australia, and most countries across the world.

NPT is used in the United States and Canada.

Are there any other differences?

NPT and BSP have a slight difference in the designs, making them incompatible with one another.

NPT have flat peaks and valleys and a 60 degree angle of the thread

BSP have rounded peaks and valleys and a 55 degree angle of the thread.

BSP

BSP standards for British Standard Pipe, and uses the Whitworth thread form. They have the designations BSPT for tapered threads, and BSPP for parallel threads. This has been adopted as standard in plumbing and pipe fitting across most of the world.

NPT

NPT stands for National Pipe Taper and uses the Sellers thread form.

It is sometimes possible for a NPT male to appear to fit into a BSP fitting (or vice versa) but it is important to note that they will not seal and may experience dangerous leakage or catastrophic failure.

When should you use BSP or NPT?

It will depend on whether you’re using something manufactured in the US or Canada, when you should use NPT fittings, or elsewhere in the world, when you should most likely be using BSP fittings.

Is NPT or BSP better?

Neither system is better than the other and both have been in use for over a century. Despite having different designs, both types of thread are equally effective – generally the only reason for choosing one over the other is where it has been manufactured and is being used.

If they’re so similar, why do both exist?

The need for a standardised screw thread came about during the Industrial Revolution, to make sure the increasing number of manufacturers were able to create compatible products.

In 1841, Briton Joseph Whitworth proposed a thread design that was adopted by railroad companies and became the national standard across the UK. It was used in the United States for a time, but was later usurped by the Sellers design.

In the US in 1864, William Sellers proposed a set of standards for nuts, screws, and bolts. His design was popular thanks to the 60 degree angle being easy for machinists to produce. It was adopted for work done under government contracts and that influence allowed it to become the national standard in the US.

What are they used for?

Tapered threads are used because they can be pulled tight to make a fluid-tight or airtight seal, unlike straight threads.

This means they are often used for pipes that transport liquids, steam, gases, and hydraulic fluids – which makes them applicable to a huge range of industries.

They can be manufactured from a range of materials, including steel, bronze, brass, cast iron, and plastics.