I'm replacing leaf spring brackets on a 92 F150, the bolts that came with the bracket appear to be M10, but I've seen reference elsewhere to replace these rivets with 7/16 grade 8. What is correct here, I already have one bracket on and bolted down with the M10 and it fit fine and the bolts were slighly loose in the holes but not excessive I didnt think. Should I take this back off and ream the holes and replace with 7/16?

Perhaps the 7/16 were replacements for other rivets like in cross members etc and the M10 are ok for the hanger?

 

7/16 should fit without having to widen the hole. Generally, the tighter the fit the better.
But I'd hope that the manufacturer of these brackets would only use m10 bolts if they were an appropriate option. So you're probably fine.

 

You'll want the tightest fit for the hole. If a 7/16 will fit, that would be a better option. I'd probably want to use a grade 8 for this, but there is some consideration of hardness in some suspension applications. Grade 8 bolts are potentially more brittle than a grade 5, so using these bolts where shear is an issue could be problematic. That's why Ford uses rivets instead of bolts.

I never trust a manufacturer for supplying hardware, btw.

I'd also use a flanged bolt and nut for any suspension fastening.

I use aircraft grade bolts when replacing suspension brackets. They're more expensive and a little more work to come by, and I'd probably never have a problem with a grade 8. But to me, it's worth it.