I am putting a set of seat belts in I purchased from seatbelt planet and I have a question on the receiver which bolts to the tunnel. Do they use shouldered bolts? All the shouldered bolts I have are a larger diameter, not sure if I should have them turned down or find different bolts.
Thanks

Make contact with the supplier.
Are the holes in the new belt hardware too small ?
Serious issue

Don't know either but I'll be doing this as well in 8-10 days. I did ask Mike @ Seat Belt Planet about their hardware kit. He said theirs were 1/2" x 27thd bolts. No metric bolts were available from them.

I'm not sure about the shoulder-bolt question, but the bolt size has been discussed at length here over the years.

The seat belt bolts are US sized 7/16-20 (apparently a US standard size required by law on all cars). They are not metric, although apparently an 11mm x 1.25 bolt is close enough that it also works.

I just installed their seat belts this past weekend. Yes, the receptacle hole is too small by about 1/16" and I had to drill it out. OTOH you could use as is if you want the receptacle rigidly fixed in place.

I emailed Mike at seatbelt planet and he said they were unaware but would make note for the future

I think I am going to get the shoulder machined down to fit the hole, I thinkk that will allow the movement while retaining the strength.

I went through this same process last week. I contacted them and the guy told me they only have one size hole and if you want a different size it will need to be drilled out. Not that big of a deal in the larger scheme of things. Just have to go buy the right size drill bit.
The customer service seemed good at seatbelt planet. I had called about another issue and after a little esplaining, a new set is on the way. Hopefully in time for my first DE