British Standard Pipe

British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread.

It has been adopted as standard in plumbing and pipe fitting, except in North America, where NPT and related threads are used.

Two types of threads are distinguished: These can be combined into two types of joints: The thread form follows the British Standard Whitworth standard: At least 41 thread sizes have been defined, ranging from 1⁄16 to 18, although of these only 15 are included in ISO 7 and 24 in ISO 228.

[3][4][5][6] The size number was originally based on the inner diameter (measured in inches) of a steel tube for which the thread was intended, but contemporary pipes tend to use thinner walls to save material, and thus have an inner diameter larger than this nominal size.

In the modern standard metric version, it is simply a size number, where listed diameter size is the major outer diameter of the external thread.