BSPT (Rc Series Pipe Taper) (British Standard Pipe Taper) This is based on the Whitworth thread form - a symmetrical V-thread with an angle of 55. BSPT has been widely adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread. The thread diameter increases along the length of the thread allowing the coupled pipes to form a seal when torqued as the flanks of the threads compress against each other. The taper is "1 to 16", meaning that for each 16 mm increase in the distance from the end, the diameter increases by 1 mm. Bottoming Taps have a lead of two threads and are used to ensure minimum thread run-out when tapping to the bottom of a blind hole. Bottoming Taps are typically preceded by the use of a Taper or Intermediate Tap.