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What is a parallel or taper thread?

Published 10 December 2015 in

A parallel or straight thread (commonly BSPP – British Standard Pipe Parallel thread) has a constant diameter and is denoted by the letter G.

A taper thread (commonly BSPT – British Standard Pipe Taper thread) has a diameter which increases or decreases along the length of the thread and is denoted by the letter R.