3-point seat belt mounting bolt in early 66

[stonekutter]

Hi folks:

I own a March '66 912 and hoping folks here can help. Mine came with a 3-point mounting point however the bolt size is not 7/16 #20 as many of the 69 and later cars.
I bought 3-point seat belts from SeatBeltPlanet but am having heck of a time finding the right bolt. Does anyone know what the bolt size is and whether there is a part available for it?

Photo of the mounting point: https://photos.app.goo.gl/MKoAiNaeZvEocGLp7
Looking at this older post it seems that the threads are M08x45. Is that accurate?

Some options I thought about:

• Find a bolt that would hold a fit that thread. If yes, does anyone have a link to someone selling it?
• Can I use tap and die set to made the hole wider to fit a 7/16 #20?

Any other things I can do? Thanks in advance!

[D Zimmer]

It looks like there has been a repair with a Helicoil thread insert. An M8x1.25 thread has the same pitch as the 7/16 x20 thread that was there. I would prefer to have the 7/16 bolt in there. If you think there is enough material there, you can pull the thread repair coil out and drill and tap for a thread insert for a 7/16-20.

[stonekutter]

Thanks. Were Helicoil thread inserts factory installed for non-US cars? My car was originally shipped to Mexico in 1966 and imported into California in 1973 (based on the earliest tags and Kardex).
AFAICT, that part of the car hasn't had any work done to it.

As an alternative, what if the knob was made of stainless steel and holding it in place using a 35K psi M8 bolt from McMaster. I can then use a snap hook seat belt and I won't have to worry about steel on aluminum contact.