What are the differences between BSP (British Standard Pipe) and NPT (National Pipe Taper) threads?
SP (British Standard Pipe) and NPT (National Pipe Taper) are two of the most commonly used thread standards for connecting pipes and fittings, but they are not interchangeable due to differences in thread angle, pitch, shape, and sealing method.
Here’s a breakdown of the main differences:
Thread Profile and Angle
| Feature | BSP | NPT |
|---|---|---|
| Thread Angle | 55° | 60° |
| Thread Shape | Rounded peaks and valleys | Flat peaks and valleys (more triangular) |
Tapered vs. Parallel
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BSP has two types:
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BSPT (British Standard Pipe Taper): Tapered threads (similar to NPT)
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BSPP (British Standard Pipe Parallel): Parallel threads
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NPT is always tapered
Functionally:
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Tapered threads (NPT, BSPT) create a seal by wedging the male and female threads together, often with a sealant like Teflon tape or pipe dope.
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Parallel threads (BSPP) require a sealing washer, o-ring, or bonded seal to make a leak-tight joint.
Size and Pitch
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Both use inch-based nominal sizing, but the thread pitches differ.
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Example: a 1/2″ NPT fitting has 14 threads per inch (TPI), while a 1/2″ BSP fitting has 14 TPI—but because of the angle and shape, they do not match up.
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Compatibility
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Not interchangeable due to:
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Different thread angles
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Different sealing methods
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Slight dimensional differences
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Trying to connect an NPT male to a BSPP female fitting will often result in:
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Cross-threading
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Leaks
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Damaged fittings
Usage Regions
| Region | Standard |
|---|---|
| USA, Canada, Mexico | NPT |
| UK, Europe, Australia, New Zealand, Asia | BSP |
✅ Pros and Cons Summary
NPT (National Pipe Taper)
Pros:
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Common in North America
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Self-sealing taper
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Easy to source in the U.S.
Cons:
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Can leak without sealant
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Over-tightening can crack fittings
BSP (British Standard Pipe)
Pros:
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Widely used internationally
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BSPP allows for secure, flat-face sealing with o-rings
Cons:
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Can be confusing due to BSPP vs BSPT distinction
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Not compatible with NPT
Quick Tip
When buying or selling fittings internationally (especially for irrigation, fluid handling, or machinery), always double-check the thread type. Even if the size “looks right,” the thread profile won’t be.
