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The British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used.
Two types of threads are distinguished:
These can be combined into two types of joints:
A list of 16 thread sizes are defined by the standards, ranging from 1⁄16 to 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 in the modern metric version of the standard, it is simply a size number.
|Corresponding pipe||Tapping drill|
The major diameter listed is the outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" from the small end of the thread. The taper is 1 to 16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.
These standard pipe threads are formally referred to by the following sequence of blocks:
Threads are normally right-hand. For left-hand threads, the letters "LH" are appended.
Example: Pipe thread EN 10226 Rp 2½
The terminology for the use of G and R originated from Germany (G for gas, as it was originally designed for use on gas pipes; R for rohr (meaning pipe).)