I have been trying to duplicate some threads on mid 1950's vintage Japanese model engines and find that the threads do not fit into current Japanese thread standards. In particular one size is almost exactly a 5-40 thread while another is just a few thousands larger in major diameter than a 12-32 thread. For shallow holes the 5-40 and 12-32 taps work but for deeply taped holes binding occurs. I was hopeful that someone knows where one can obtain info and preferably suitable taps. The threads are definitely not metric or an early British standard.
Thanks
Bob