BSPF is a very old BS-2779 screw
thread designation which 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 threads.
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 (BSPM)
screw thread designation got wide acceptance and in general the
British Standard Pipe Parallel (BSPP)
screw thread designation continued to be the common default thread
Many people now use British Standard Pipe (BSP)
to refer 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
screw thread or British Standard Pipe Taper (BSPT)
screw thread. I have seen it both ways.