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Also referred to as Whitworth threads, the BSP thread type fittings seal using metal to metal angled surfaces or a combination of metal to metal and an O-ring. The angle of the sealing surfaces is 60° for both forms. There are two popular thread forms, British Standard Pipe Parallel (BSPP) and British Standard Pipe Tapered (BSPT).
MALE: The measurements for the male are taken from the outside of the threads.
FEMALE: For the Female, the measurement is taken from the inside of the threads.
The below diagram shows both where to take measurements from and the size dimensions.