From an article I'm writing:
Yanmars are built in Japan
, and Japan
uses the British Standard Pipe Thread (BSPT) standard. Danger
lies in the fact that the threaded shaft on most of these sensors are 1/8” and the NPT and BSPT versions are very nearly the same. The thread density and coarseness are the same; but the American version cuts the threads at 60⁰ while the British version uses 55⁰. One will screw into the other, but it will leak. Luckily, adding domestic sensors to Japanese cars is common enough that at least one retailer, Pegasus Auto Racing
Supplies, stocks NPT sensors as well as the NPT/ BSPT adaptors. And they cost a lot less than the marine
versions. For my 2GM
Yanmar, the oil pressure sensor cost just $40, the temperature sensor, a measly $17.
Note: There is a third pipe standard, British Standard Parallel Pipe (BSPP). Both NPT and BSPT are tapered, meaning the threaded hole is cone shaped. BSPP threads have instead parallel sides. And like a spark plug
, adapters for engines using this standard must use a crush washer in order to seal.