Originally Posted by
MrToad
NPSM seals between a groove in the female thread (the block) and a flange on the male thread.
BSPP with O-ring (Gx/x") has a groove on the nut of the male fitting to hold the O-ring in place and seals against a flat surface on the female thread.
The threads in the Storm, as well as the MCW30, MCW60 and so on are 1/4" NPSM, hence he "wide flange".
And FYI, BPSS is many things, but none of them directly related to plumbing. However, BSPP is British Standard Pipe Parallel, (short form: BSP, as if it's not tapered, or BSPT, then it must be parallel).
Now that I've let some steam out, back to my personal war of attrition with the rodents...