Rear Sproket bolt size

I know they should be 8mm on my 1980 390CR but the guy I bought it from had 6mm in then, nice!
The confusing part for me is the hub holds the 6 lose but won't take the 8. The sprocket will. I don't believe it was filled in with weld or a threaded insert put in.
Any thoughts?
Thanks in advance!
Pete

Non metric thread as OE (?) or have the hubs been painted or powder coated?

No threads in the holes. No on the re-paint or powder coating either. I see your point on if they were it would make the holes tight but the holes are ovaled some from the small bolts going forward and backward. Like it was a good tight 6 before being worn.

definetly 8s mate 6s wouldnt be strong enough, it wouldnt make the hole smaller,just run a 8mm bit through and clean hole up and they will be fine

Some hubs must have smaller than 8 mm bolt holes as generally before there were countersunk holes in the sprocket the sprockets had two sizes of holes. The smaller ones probably were for 6 mm. Can't say I have ever seen a hub with that size hole however somehow perhaps you have one.

Thanks Gang! Patgas, I plan on doing exactly what you said.