I'm sitting here with my McMaster-Carr catalog and found the section describing the difference between these two kinds of pipe thread.

National Pipe Taper (NPT) threads are most widely used in North America. The distinguishing characteristics are that they have flattened peaks and valleys with the valley angle being 60 degrees.

British Standard Pipe Taper (BSPT) threads are the European equivalent to NPT threads. The peaks and valleys are rounded and the valley angle is 55 degrees.

Pipe size, Pipe OD, threads per inch NPT, threads per inch BSPT:
1/8", 0.405", 27, 28
1/4", 0.540", 18, 19
3/8", 0.675", 18, 19
1/2", 0.840", 14, 14
3/4", 1.050", 14, 14
1", 1.315", 11.5, 11

So in a nutshell, I hope this is enough information to discourage people from jamming NPT fittings into their Honda blocks!

 

the back of the block is 1/8 bspt...(i know that)

how about the hole near the vtec solenoid on a
b series VTEC head...is it the same ..?????

thanks much.!

 

im not sure exactly what it is... but is is NOT a tapered plug

 

so does anyone know why a 1/8" BSPT male will go into a 1/8" NPT female no problem? It makes sense to me that it doesn't work the other way around but I can't figure out why it does work this way...

-Xerxes