ptsg
Super Member
3/4" BSPP is most likely the right one. The Japanese also use the JIS fittings a lot, which is essentially a BSPP thread with a 30 degree taper to seal, similar to JIC.That's right. Thank you for the correction. I must have suffered a brain lapse. In Japanese machines, most interally threaded holes into an iron casting use BSPT, which is British Standard Pipe Tapered. But this one shouldn't be tapered at all. My mistake.
Since the 3/4" NPT fit so well, I suspect it is BSPP - British Standard Pipe Parallel. That is also used by Japanese equipment for threading cast iron.
There may be a close metric. I'm not sure. Not knowledgeable on course metric threads.
Sorry for the confusion; I erased my previous post.
rScotty
The NPT stuff will usually thread on BSPP, although the thread pitch is off a little bit but still works.
3/4" BSPP is also very close to M27x1.75. Converting to metric, it ends up like 26.44mm x 1.81. While M27x1.75 is used more on injectors, M27x2 is used a lot on hydraulics.