The main difference between NPT and BSP threads lies in the thread angle (NPT: 60°, BSP: 55°) and in the shape of the thread profile (NPT: tapered, self-sealing; BSP: parallel for internal threads and tapered for external threads, requires sealing). These differences make the two types of threads incompatible with each other and require a special adapter for a connection.
NPT Thread
- Thread Angle:60 degrees
- Profile:Tapered thread
- Sealing:Self-seals through the deformation of the female thread (self-sealing)
- Distribution:Mainly used in North America
- Application:Popular in high-pressure applications
BSP Thread (British Standard Pipe Thread)
- Thread Angle:55 degrees
- Profile:Flat peaks and rounded valleys; the external thread type (BSPT) is tapered, but the internal thread type (BSPP) is parallel
- Sealing:Requires a separate seal (seal tape, washer or sealant) for a secure seal
- Distribution:Widely used worldwide, especially in Europe, Asia, and Australia
- Application:Common in Europe, Asia, Australia, and other regions with a metric system, as well as in low-pressure applications
Important Aspects
- Incompatibility:
NPT and BSP threads are not compatible with each other due to their different angles and profiles and must not be directly connected, as this can lead to leaks. - Marking:
The shape of the threads (tapered vs. parallel) can allow for easy differentiation in external threads, but is more difficult to recognise in internal threads.