NPT (National Pipe Thread) and BSP (British Standard Pipe) threads are two common pipe and fitting seal fitting thread standards that differ in several ways.

The following is a detailed comparison of these two threads:

NPT Thread Definition and Standards:

Abbreviation for National (American) Pipe Thread, a 60-degree tapered pipe thread that belongs to the American standard. By the American Standards Institute (ANSI/ASME) development and management.

BSP Thread Definition and Standards:

It is the abbreviation of British Standard Pipe, which is the British standard, formulated and managed by the British Standards Institution (BSI).BSP thread is divided into three kinds: BSPP (Parallel Cylindrical Pipe Thread), BSPT (Tapered Pipe Thread) and BSPF (Fine Thread Pipe Thread).

NPT thread tooth angle and taper:

The tooth angle is 60 degrees with a taper, this design helps with sealing because when threaded connections are made, they seal better as the threads become tighter.

BSP Threads Tooth Angle & Taper:

BSPP: Internal threads only, equivalent to domestic 55 degree cylindrical (parallel) pipe threads, no taper.
BSPT: Tooth angle of 55 degrees, with 1:16 taper, commonly used in Europe and Commonwealth countries in the water and gas pipe industry.
BSPF: British fine-pitch pipe thread, mainly used for jointing.

NPT thread application characteristics:

Commonly used in North America and the use of ANSI specification occasions.
Have good sealing performance, commonly used in the transportation of liquids, gases, steam and hydraulic fluids.
Designed for metal-to-metal sealing, additional sealant is usually not required.

BSP thread application characteristics:

More common in the UK, Australia, New Zealand and other countries and regions.
BSPT and BSPP are used for sealing joints, while BSPF is used for general jointing.
BSP threads use a gasket or sealant to provide a seal.

NPT Thread Size:

Sizes are usually expressed in inches, such as 1/8 inch, 1/4 inch, etc. The marking includes the thread characteristic code (NPT), thread size code and rotation code.

BSP Thread Size:

Dimensions are usually expressed in metric units, such as millimeters or inches. the marking of BSP threads also includes the corresponding characteristic designator and size designator.

Conclusion:

When selecting and using BSP threads, ensure that all components conform to the same standard to ensure compatibility and sealing.
BSP threads are not compatible with other standards such as NPT (American National Standard Pipe Thread) and therefore cannot be used interchangeably.
When installing BSP threads, proper tools and techniques should be used to ensure a proper and tight threaded connection.
The choice of NPT or BSP depends on the specific application scenario, regional standards, and the required sealing performance.