BSPP is an old BS-2779 screw
thread designation which is no longer authorized. British Standard
Pipe Parallel (BSPP) is now correctly designated as G and defined
The following is what I have been told by some old-timers in the
British gage industry:
The British Standard Pipe Parallel (BSPP) screw thread was changed
to British Standard Pipe Fitting (BSPF)
screw thread to remove the confusion between the like sounding BSPP/BSPT
screw thread designations.
The new BSPF
screw thread designation caused a different confusion in the pipe
industry when it was associated with the ANSI Dry-seal taper pipe
screw threads. The ANSI taper pipe screw thread series has National
Pipe Taper (NPT) screw thread which is the common taper pipe thread
and National Pipe Taper Fuel (NPTF) screw thread which is the dry-seal
version of the taper pipe thread. Both of these ANSI pipe screw
threads are taper pipe screw threads. Thus the British Standard
Pipe Fitting (BSPF)
parallel screw thread was again being confused with taper pipe screw
To solve this newest confusion the designation was changed in a
later version of BS-2779 to British
Standard Pipe Mechanical (BSPM)
screw thread. This new designation was intended to communicate that
the parallel screw thread was similar to the ANSI National Pipe
Straight Mechanical (NPSM) parallel screw thread.
Neither the British Standard Pipe Fitting (BSPF)
screw thread designation nor the British Standard Pipe Mechanical
screw thread designation got wide acceptance and in general the
British Standard Pipe Parallel (BSPP) screw thread designation continued
to to be the common default thread designation.
Many people now use British Standard Pipe (BSP)
to refer the the current G-series screw thread, but caution is advised
when reading a screw thread designation labeled BSP.
A British Standard Pipe (BSP)
screw thread could be a shortened version of British Standard Pipe
Parallel (BSPP) screw thread or British Standard Pipe
Taper (BSPT) screw thread. I have seen it both ways.