The Difference Between BSPT, NPT and BSPP Threads

When it comes to sealing pipe fittings—especially in stainless steel systems—choosing the correct thread type is crucial to avoid leaks, ensure compatibility, and meet pressure requirements.

The main difference between BSPT, BSPP, and NPT threads lies in their shape and sealing mechanism:

• BSPT – A tapered thread from the BSP family, features a 55-degree flank angle.
• BSPP – A parallel (straight) thread from the BSP family, maintains the same diameter throughout.
• NPT – Another tapered thread, but follows U.S. standards, with a 60-degree thread angle.

We’ll explore what these differences mean in practice—and how to choose the right one for your system—throughout the rest of this guide.

BSPT (British Standard Pipe Thread)

BSPT stands for British Standard Pipe Tapered. This type of thread narrows as it moves toward the end, forming a mechanical seal as it tightens. This allows the male and female components of the thread to fit together since the adapter stretches the component it is fitted to with enough force to withstand pressure.

A sealing compound or thread tape is commonly used to ensure that components are sealed properly, providing leak-free performance.

NPT (National Pipe Thread)

NPT stands for National Pipe Thread, a standard mainly used in the United States. Like BSPT, it’s tapered, but the thread angle is 60 degrees, whereas BSPT has a 55-degree angle. This small difference means NPT and BSPT aren’t interchangeable, even though they look similar.

NPT threads also seal through tightening, but they can leak if over-tightened or if too much sealant is used.

BSPP (British Standard Parallel Pipe)

BSPP stands for British Standard Pipe Parallel. Unlike BSPT, BSPP threads keep the same diameter all the way through. Because of this, BSPP connections need a bonded seal ring to ensure a leak-proof seal.

It’s commonly used in low-pressure or hydraulic applications where a flat surface seal is preferred.

BSPP vs BSPT: What’s the Real Difference?

Though both fall under the British Standard Pipe category, BSPP and BSPT differ fundamentally:

A question we often get is: Can you mix BSPP and BSPT fittings?

What we say is—it depends. Think of it like this: if you’ve got a tapered male thread (like BSPT), it can be used with either a tapered or parallel female, but a parallel male (BSPP) only works with a parallel female. It won’t seal properly with a tapered thread.

Choosing between BSPT, BSPP, and NPT fittings is more than just a technicality—it’s essential for ensuring safe, efficient, and leak-free systems. If you’re not sure which thread type suits your application, our expert team at Anglo Stainless is here to help.

With over 40 years of experience in stainless steel fittings, we stock a comprehensive range of BSPT and BSPP fittings and offer trusted advice for industrial and commercial applications.

Call us today at 01924 430 044 or contact us online to get started.