BSPM = British Standard Pipe Mechanical

BSPM = British Standard Pipe Mechanical

BSPM is an old BS-2779 screw thread designation which is now correctly designated as G and defined in ISO-228.

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 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.

A final word: BS-2779 has been rescinded and should no longer be used. If you read a requirement for BS-2779, it should be translated to read ISO-228.

Comments about the above statement can be sent to: office@gagecrib.com