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When purchasing valves or piping components, you often encounter thread standards like NPT, PT (BSPT), and PF (BSPP). If you're new to these, it's natural to wonder: "They all look similar - what's the difference?"
In practice, mismatched thread standards can result in assembly failures or leaks - and in severe cases, damaged threads that require replacing the entire component. Today, we'll clearly explain the differences between NPT, PT (BSPT), and PF (BSPP) and guide you on how to choose correctly.
| Category | NPT | PT (BSPT) | PF (BSPP) |
|---|---|---|---|
| Thread Form | Tapered | Tapered | Parallel |
| Taper | 1:16 (approx. 1°47′) | 1:16 (approx. 1°47′) | None |
| Thread Angle | 60° | 55° | 60° |
| Sealing Method | Thread-to-thread seal | Thread-to-thread seal | Separate gasket or O-ring required |
| Representative Standard | ANSI / ASME | BSPT | BSPP |
NPT is the most widely used thread standard in the United States. Its tapered design - where the thread narrows toward the end - creates a natural seal as it is tightened.
The key characteristic is a thread angle of 60°.
Commonly found on American-made industrial equipment and valves.
PT is the most commonly used thread standard in South Korea. Based on the British BSPT standard, it is also a tapered thread - similar to NPT - but the thread angle is 55°, which is the key difference.
Predominantly used in domestic industrial valves, piping, and pneumatic equipment.
PF (also called BSPP) is a parallel thread. Unlike NPT and PT, it does not seal via the threads themselves - sealing relies on O-rings, gaskets, or packing. This means tightening the thread alone does not achieve a seal; separate sealing components are required.
This is where most people get confused. Both are tapered threads, so they appear similar at a glance - but their thread angles differ:
Forcing connection between these two standards will result in damage or leakage. NPT and PT must never be interchanged.
Just because threads look similar doesn't mean they are interchangeable. NPT and PT (BSPT) are both tapered but have different thread angles, while PF (BSPP) is a parallel thread with an entirely different sealing method.
When selecting valves or fittings, always verify the thread form (tapered/parallel), thread angle, and applicable standard to ensure a leak-free, safe installation.
VALVEPARK will continue to provide practical technical information and solutions to help professionals on the job site make the right decisions.
