The pipe plugs looked like tapered NPT pipe plugs, one 3/8 and two 1/2? Checked the thread pitch. Male to male nipples installed the same into the line distribution blocks. 1/2 pipe threads of BSPT and NPT are so similar that they fool experts. I知 no expert. Hope I didn稚 mess up. No leaks yet.
Have encountered BSPT on other hydraulic fittings and even BSPT on hydraulic grease fittings on my other Kubota tractors. Been careful not to cross thread.
As you know - but for those who don't.... Many Asian manufacturers who use the metric standard for most every nut, bolt, and measurement on their tractors will use the British tapered pipe thread - called BSPT, for all their tapered pipe thread. You see this a lot especially where tapered pipe threads are factory cut into a cast iron motor or transmission block.
For cars, tractors, and industrials mfg. in Japan the practice is "almost" 100%.
You'll also see this BSPT thread in water jackets and oil fittings in otherwise metric block castings.
Matching threads is one of the hassles when putting in a block heater or piping oil/water to analogue gauge sets.
But not always.... There is no real standard practice so you have to check. On my M59 the tapered pipe nipples that hold the hydraulic oil filters into the bottom of the cast iron transmission housing appears to be NPT X NPT. That seemed so odd to me that I took them out to compare. Well, it was hard to decide. They weren't fitted well at the factory and had come loose. But I'd have to call them both NPT X NPT.
Since common hydraulic, water, and fluids plumbing in the US uses the very similar NPT threads, if we are doing mods them we like to do a deliberate switch from a from BSPT to the standard NPT thread. Easy way to do this is to start with an BSPT X NPT adapter nipple or similar male/female adapter and then after that we can stay with our normal NPT fittings. McMaster-Carr has the adapters online, but you can often find them at car parts or hardware stores if you ask.
The threads are similar enough that you can force fit an NPT-M plug into a BSPT-F fitting. Usually it's hard to do, it won't go in very far, and will require a lot of torque to advance the threads after the first few turns. I know because I've not only seen it done, plus I'm sure I did it myself as a young mechanic before I realized the difference.
Sometimes this cross thread will leak, but just often enough they won't. If suspect you've done that and it doesn't leak, then my advice is don't remove it. Crossing the thread types does tend to ruin the block threads enough to make replacement somewhat chancy.
Now that I know the difference, I keep a handful of sizes of NPT X BSPT nipples & Male/Female adapters in the tool box to use for thread ID. The best way I know to do the thread ID is by seeing how well the threads will mate just by hand fitting. The difference is sometimes too small for me to measure any other way.
As you say, sometimes it's difficult to decide just what threat it is that you are dealing with.
Hydraulic grease fitting threads are even more difficult to decipher. I've still not got those figured out. Some are tapered, others are are parallel threads but in several diff. types.
rScotty
