British Standard Pipe Taper (B.S.P.T.) threads are sealed by interlocking a male and female component, with contact on the thread flanks.

• A. The threads are sealed by interlocking a male and female component with contact on the thread flanks.
• B. They are standard metric pipe threads with no taper.
• C. They are a form of square thread.
• D. They are used for decorative purposes.

Answer: (A)

BSPT threads are tapered pipe threads that screw together so the mating surfaces press against each other as you tighten. The taper causes a wedging action, and the seal is formed by metal-to-metal contact along the thread flanks as the threads engage. In practice, sealing compounds or PTFE tape may be used to fill minor gaps, but the core sealing mechanism is the interlocking tapered threads making contact on the flank surfaces. The other descriptions don’t fit: there is a taper, it isn’t a square-thread form, and they aren’t for decoration.