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NPT (national pipe thread) is the standard pipe thread in the USA.
FPT (FMPT) and MPT (MNPT) simply denote female or male. Virtually all the NPT threads that you will find are 'tapered'.
BSPT (British Standard Pipe Tapered) or BSPP (British Standard Pipe Parallel) are the common pipe threads used in the uk and also in Europe.
'Metric' is a broadly used term to describe threads used in europe
You rarely need an adapter because NPT fittings work just fine with BSPP or BSPT
You may have been told you should not mix BSPP with BSPT or with NPT you can ignore this crap in low pressure systems,
say under 100psi, is a well safe margin
you can often mix NPT fittings with BSPP or BSPT For example 1/2" NPT fittings work ok with 1/2" BSPP
In this case, you are mixing tapered with parallel, so use PTFE tape. the same is true for 1" NPT with 1" BSPP
Tapered vs Parallel Threads.
If you look at male NPT threads, you will notice the diameter of the fitting is tapered narrowest at the end.
Parallel threads do not have a taper. The most important thing to understand is that tapered threads form a seal differently than parallel threads.
Fittings with tapered threads seal on the threads. Use PTFE tape on these type of threads to help make a good seal.
Why does NPT work with BSPP?
1/2"NPT to 1/2"BSPP. Both have 14 threads per inch so they match up quite well. The primary difference is in the pitch (angle of the thread) which is 60? to 55?. Use a PTFE tape and they screw together and seal OK.
3/4"NPT works well with 3/4" BSPP as well since the threads per inch is the same, 14.
So on LOW PRESSURE systems these threads work OK!
suppose! the yanks have got to have their own veriation,
of course there is a little more to it than that!
ie variouse TPI on size
BUT for our applications things are fine 
Edited by BENROSS on 22nd Mar, 2005.
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