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NPT vs. BSPT: What is the difference?

16. June 2026

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At first glance, NPT and BSPT look similar. Both are tapered pipe threads, and both are used for pressure-tight connections. That is exactly why they are repeatedly confused in practice. The problem often only becomes apparent during assembly: The connection can initially be screwed in a short way, but it does not sit cleanly and, in the end, does not seal reliably. If you want to reliably distinguish NPT from BSPT, you therefore need to look not only at the diameter, but also at the thread profile, flank angle and pitch.

“For pipe threads, it is not enough for a connection to look visually similar. What matters is that the thread form, standard, and tool are precisely matched.”

Simon Siebert

Head of Production & QS

What are NPT and BSPT?

Anyone who works with pipe threads will sooner or later come across the terms NPT and BSPT. Both thread types are used wherever connections need to be tight, load-bearing and reliably screwable.

NPT is the tapered US pipe thread according to ASME B1.20.1. It uses a flank angle of 60 degrees. BSPT belongs to the British or internationally established pipe thread system and is based on the Whitworth profile with 55 degrees.

At first glance, this difference seems small. In practice, however, it is crucial. It is not only the designation that is different, but also the thread profile and, in many sizes, the pitch. This is exactly why NPT and BSPT do not fit together cleanly simply because they look similar.

Why are NPT and BSPT so often confused?

The confusion does not come out of nowhere. Both threads are tapered, both are used for pipe connections, and both seal via the thread. In everyday practice, this can quickly create the impression that the two systems can be combined with each other if necessary.

But that is exactly not the case. An NPT thread has a flank angle of 60 degrees, while a BSPT thread has a flank angle of 55 degrees. In addition, the shape of the thread turns also differs. These differences mean that female and male threads can sometimes be started, but they do not work together cleanly.

This is particularly tricky in workshops, assembly and maintenance. If a connection initially engages, it can quickly appear to be suitable. From a technical point of view, however, that does not mean it is correct.

What is the difference in detail?

The most important difference lies in the profile. NPT and BSPT look similar, but they are not based on the same thread geometry.

NPT is the tapered US pipe thread according to ASME B1.20.1
it works with a flank angle of 60 degrees
BSPT belongs to the British or internationally established pipe thread system
it is based on the Whitworth profile with 55 degrees

Then there is the pitch. Here, too, there are differences in many sizes. Typical examples are:

1/8": NPT with 27 TPI, BSPT with 28 TPI
1/4": NPT with 18 TPI, BSPT with 19 TPI
1": NPT with 11.5 TPI, BSPT with 11 TPI

These exact deviations are what make the issue so critical in practice. The connection can often still be started and may initially seem to fit, but it does not run cleanly and, in the end, does not seal reliably.

Is BSPT the same as BSPP or G thread?

No. This is also frequently mixed up in practice. BSPT is the tapered variant in the BSP system. BSPP or G thread, by contrast, is parallel.

The difference is important because it also changes the sealing principle. BSPT seals via the thread. BSPP or G thread, on the other hand, usually requires an additional seal or an O-ring.

So anyone who only looks at the designation “BSP” can easily miss a crucial difference.

Why should NPT and BSPT not be mixed?

In practice, this is one of the most common mistakes. A connection engages, so it is tightened further. This is exactly where stresses, damaged thread turns and leaks occur.

The reason is simple: different flank angles, a different profile and, in some cases, a different pitch prevent clean flank contact. The thread may initially appear to fit, but it does not work together as it was designed to do.

That is why VÖLKEL relies on a clear separation of the systems: NPT remains NPT, BSPT remains BSPT. Only when all components are properly matched to each other will the connection work reliably not only during screwing in, but also later in use.

How to identify the difference in the workshop

To avoid confusion in the first place, a systematic approach helps in practice:

Step 1: First check whether it is a tapered pipe thread
Step 2: Then determine the diameter and pitch
Step 3: Next, clearly assign it to NPT or BSPT
Step 4: Finally, use the correct threading tool

A thread gauge is an especially important aid here. Technical drawings, markings and parts lists also help.

Which taps do you need for this?

The choice of tool is ultimately just as clear as the standard itself. For an NPT female thread, you need an NPT tap. For a BSPT female thread, the appropriate Rc (BSPT) tool is used. For external threads, the same principle applies with the corresponding die or threading tool.

This is often where it is decided in practice whether everything will run smoothly later or whether problems are already built in.

Available immediately: suitable taps for NPT and BSPT from VÖLKEL

At VÖLKEL, you get not only individual taps, but the right solution for both systems: NPT and Rc (BSPT) tapered. Many variants are directly available from stock, so you can produce pipe threads according to the standard and without unnecessary delay.

And if your application requires a specific dimension or design, VÖLKEL remains just as flexible. This means you get exactly the threading tool that matches your thread system and your application.

Conclusion

NPT and BSPT are not two designations for the same thread, but two different tapered pipe thread systems. They look similar, but they differ in flank angle, profile, standard and often also in pitch. This is exactly why they must not be mixed in practice.

Anyone who wants to produce or identify pipe threads reliably should therefore not rely only on first impressions, but should check the system properly. With the right tool from VÖLKEL for NPT and Rc (BSPT), this can be done reliably.