BSP vs NPT: How to Tell British and American Pipe Threads Apart
NPT is the American taper pipe thread in ASME B1.20.1. BSP is the British pipe thread, made as BSPT (taper, ISO 7-1) and BSPP (parallel, ISO 228-1).
Quick answer: BSP and NPT are not interchangeable. NPT has a 60° thread angle and BSP has 55°, and the threads per inch differ in every size except 1/2″ and 3/4″. Count the threads per inch and measure the outside diameter, then match both in the chart below.
BSP vs NPT at a Glance
| Feature | BSP | NPT |
|---|---|---|
| Thread angle | 55° | 60° |
| Thread shape | Rounded crests and roots | Flattened crests and roots |
| Taper | BSPT tapers 1 in 16. BSPP is parallel | Tapers 1 in 16 |
| Seals with | BSPT: sealant on the threads. BSPP: a bonded seal, an O-ring or a 60° cone seat | Sealant or PTFE tape on the threads |
| Markings | G (BSPP). R, Rc and Rp (BSPT) | NPT or NPTF |
| Standards | ISO 228-1, ISO 7-1, EN 10226 | ASME B1.20.1 |
| Where it is used | UK, Europe, Australia and much of Asia | United States and Canada |
BSP vs NPT Size Chart
Both threads are named by nominal pipe size, not by what they measure. Go by the threads per inch first, then the outside diameter of the male thread.
| Nominal size | BSP threads per inch | NPT threads per inch | BSP outside diameter | NPT outside diameter |
|---|---|---|---|---|
| 1/8″ | 28 | 27 | 0.383″ (9.7 mm) | 0.405″ (10.3 mm) |
| 1/4″ | 19 | 18 | 0.518″ (13.2 mm) | 0.540″ (13.7 mm) |
| 3/8″ | 19 | 18 | 0.656″ (16.7 mm) | 0.675″ (17.1 mm) |
| 1/2″ | 14 | 14 | 0.825″ (21.0 mm) | 0.840″ (21.3 mm) |
| 3/4″ | 14 | 14 | 1.041″ (26.4 mm) | 1.050″ (26.7 mm) |
| 1″ | 11 | 11.5 | 1.309″ (33.2 mm) | 1.315″ (33.4 mm) |
| 1-1/4″ | 11 | 11.5 | 1.650″ (41.9 mm) | 1.660″ (42.2 mm) |
| 1-1/2″ | 11 | 11.5 | 1.882″ (47.8 mm) | 1.900″ (48.3 mm) |
| 2″ | 11 | 11.5 | 2.347″ (59.6 mm) | 2.375″ (60.3 mm) |
Values are nominal, per ISO 228-1, ISO 7-1 and ASME B1.20.1. A tapered male thread reads slightly smaller at its tip. Verify against your part before ordering.
- 1/8″ to 3/8″: BSP has one more thread per inch than NPT.
- 1/2″ and 3/4″: both have 14 threads per inch, so these are the sizes people mix up.
- 1″ to 2″: BSP has 11 threads per inch and NPT has 11.5.
- Every size: BSP measures slightly smaller across than NPT.
How to Tell BSP from NPT in 3 Steps
- Count the threads per inch. Use a pitch gauge on a clean thread. In most sizes this settles it. A count of 28, 19 or 11 is BSP. A count of 27, 18 or 11.5 is NPT.
- Measure the outside diameter. Use a caliper across a male thread and match the reading in the chart. This gives you the nominal size.
- At 14 threads per inch, check the thread shape. In 1/2″ and 3/4″ the count is the same and the diameters are close. Hold a 55° Whitworth gauge leaf and a 60° gauge leaf against the thread. The leaf that sits in the thread with no light showing is your answer. BSP crests also look rounded, and NPT crests look flat.
Other clues: a part marked G, R, Rc or Rp is BSP. A parallel thread with a washer, an O-ring or a cone seat is BSPP, not NPT. On equipment built in the United States or Canada, a pipe thread is usually NPT. On equipment built in Europe or Asia, it is usually BSP.
Will BSP and NPT Fit Together?
No. In most sizes the threads bind before they are tight, and in the sizes where they do tighten they will not hold pressure.
| Size | What happens |
|---|---|
| 1/8″, 1/4″, 3/8″ | The pitch differs by one thread per inch. The fitting binds within a few turns |
| 1/2″, 3/4″ | The pitch matches, so the fitting starts by hand and can be tightened. The thread angles do not match, and the joint leaks |
| 1″ to 2″ | 11 threads per inch against 11.5. The fitting binds within a few turns |
Sealant does not fix a mismatch. Extra tape or thread sealant can hide the gap at low pressure. Under hydraulic pressure the joint leaks, and forcing it tighter can gall the threads or crack the port.
The same goes for the parallel thread. A BSPP fitting has nothing to seal on in an NPT port, and an NPT male thread will not seal in a BSPP port.
Joining BSP to NPT: Use an Adapter
When one side is BSP and the other is NPT, the fix is an adapter with the correct thread on each end. Seal each end the way that thread is meant to seal: sealant on NPT and BSPT, and a bonded seal, an O-ring or a cone seat on BSPP.
We stock fittings and adapters in NPT, BSPP and BSPT threads. Tell us the thread on each side and we will match the adapter. See the hoses, fittings and adapters we stock, our BSPP vs BSPT thread chart and our fitting identification guide.
Where You Find Each Thread
NPT is the pipe thread on equipment built in the United States and Canada. BSP is the usual pipe thread in the UK, Europe, Australia and much of Asia, so it turns up on imported excavators, tractors, compressors and attachments. Japanese equipment uses the same threads as BSP under JIS names. A machine sold in the United States can still have BSP ports if it was built overseas.
4 Mistakes to Avoid
- Going by the name. A 1/2″ pipe thread of either type measures more than 0.8″ across.
- Trusting a fitting that starts by hand. 1/2″ and 3/4″ BSP and NPT start on each other and still leak.
- Adding more tape. Sealant cannot make two different thread angles seal.
- Assuming NPT because the machine was bought here. Imported equipment often has BSP ports.
Frequently Asked Questions
Are BSP and NPT threads compatible?
No. The thread angle is 55° on BSP and 60° on NPT, and the threads per inch differ in most sizes. They do not seal together.
What is the difference between BSPT and NPT?
Both are tapered pipe threads that seal on the threads, and both taper 1 in 16. BSPT has a 55° thread with rounded crests. NPT has a 60° thread with flattened crests. The threads per inch match only in 1/2″ and 3/4″.
Can I use thread tape to join BSP to NPT?
Not for hydraulic pressure. Tape may slow a leak at low pressure, but the threads do not match. Use an adapter.
How do I know if my thread is BSP or NPT?
Count the threads per inch with a pitch gauge and measure the outside diameter with a caliper, then match both in the size chart above. At 14 threads per inch, check the thread shape with a 55° gauge and a 60° gauge.
Is a G thread the same as NPT?
No. G is BSPP, a parallel British thread that seals on a washer, an O-ring or a cone seat. NPT is a tapered American thread that seals on the threads.
Is NPTF the same as NPT?
NPTF is the Dryseal thread in ASME B1.20.3. It has the same angle, taper and threads per inch as NPT, with the crests and roots held to closer limits so the threads can seal without sealant. For telling BSP from NPT, treat it the same as NPT.
Can you ship BSP and NPT adapters outside the United States?
Yes. See worldwide shipping or request a quote with the destination country.
Not sure which thread you have?
Send a photo next to a ruler or caliper and we will identify it.
Sources: ASME B1.20.1 (general-purpose pipe threads, NPT); ASME B1.20.3 (Dryseal pipe threads, NPTF); ISO 228-1 (pipe threads where pressure-tight joints are not made on the threads); ISO 7-1 and EN 10226-1 (pipe threads where pressure-tight joints are made on the threads).
Last updated: November 14, 2026
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Hydraulic Hoses Near Me LLC in New Milford, CT is open 24/7. We stock Gates, Parker and Aeroquip hose and fittings and Adaptall adapters, and we ship worldwide. Mobile service covers CT, NY and MA. Call with your thread measurements or bring the old part and we will match it.