Pre-ISO Metric Fasteners

[swall]

I seem to recall that prior to ISO standards, the Japanese had their own standards for metric fastener sizes. Many of these became obsolete when metric ISO fastener standards were adopted. I am right on this? The reason I ask is that I have run across some fasteners on a Japanese 2 stroke engine (1980 vintage)that appear to be 5.5mm with a .9mm pitch (they could also be 12-28).

 

[MintJulep]

There was (and maybe still are) Japanese Industrial Standard (JIS) metric fasteners.

I think that the thread diameter and pitch matches ISO, but that for some sizes the wrench hex was different.

 

[Screwman1]

There are still JIS fastener standards; they are not obsolete,many Japanese firms still use them. The thread form is the same as the ISO standard, but head profiles are different and the materials require JIS spec steel.