stock 68 shoulder belt location bolt hole size?

[Banjo]

I've thought about putting shoulder belts in my 68 and for the life of me, I cannot figure out what size bolt goes in those holes already pre-drilled, anyone know what size/thread bolt I should buy? Maybe I'm not finding what size I need because I'm looking for grade 8, maybe I need to be looking at grade 5, because I cannot find what fits? Help my mental block please, have a seat of shoulder belts in a 5 gallon bucks I'd sure like to install this weekend maybe. Thanks, Banjo.

[MAK]

Here ya go. This is the same set-up I used in mine. I had to thread mine, it wasn't already done in my 72.
http://fordification.com/forum/viewtopi ... seat+belts