I was thinking the oil drain plug was an SAE bolt thread?

Personally I have no idea. They are still available through Nissan.

10 hours ago, Patcon said:

I was thinking the oil drain plug was an SAE bolt thread?

M16.4 - https://www.rockauto.com/en/moreinfo.php?pk=3270447&cc=1209169&pt=10231&jsn=605

That is approximately 5/8, but I'm not sure

Edited Monday at 11:47 AM1 day by SteveJ

2 hours ago, SteveJ said:

M16.4 - https://www.rockauto.com/en/moreinfo.php?pk=3270447&cc=1209169&pt=10231&jsn=605

That is approximately 5/8, but I'm not sure

I believe the OE spec tor the oil drain plug is 3/8 BSPP. The threads on mine measure 16.43mm major diameter, which is at the low end of the BSPP parallel spec, 16.662mm +0/-0.25mm. I don't have a metric 55 degree thread gauge but my 1.3mm 60 deg. thread gauge is very close to the spec pitch of 1.337mm.

https://amesweb.info/screws/bspp-thread-chart-calculator.aspx

Edited Monday at 08:44 PM1 day by CanTechZ

Yup, 7/16-20 for the seat belts. M12 is a valid spec as well from some DOT document I found 15 years ago when I was researching aftermarket replacement belts. No idea what manufacturers adopted world wide. Also curious what seat belt threads were used on the various early 60’s datsuns (411, roadsters etc).

The 1/4-28 are on the two Z hood bumper . Craziest thing I’ve ever seen. Must have been supplier determined at the time.