Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. The taper is 1:16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.

The thread form follows the British Standard Whitworth standard:

1.) Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)

2.) One-sixth of this sharp V is truncated at the top and the bottom

3.) The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r ≈ 0.1373P

4.) The theoretical depth of the thread is therefore 0.6403 times the nominal pitch h ≈ 0.6403P

British Standard Pipe Parallel thread (BSPP, originally also known as British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G (*Ref).

The thread form follows the British Standard Whitworth standard:

1.) Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)

2.) One-sixth of this sharp V is truncated at the top and the bottom

3.) The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r ≈ 0.1373P

4.) The theoretical depth of the thread is therefore 0.6403 times the nominal pitch h ≈ 0.6403P

*Ref: Learn more about British Standard Pipe