Rivnuts

[MBB]

Just mic the outside dia of the rivnut and drill to a tight fit.

 

[hotponyshoes]

Yes! this is making some kind of sense now.
7/16 - 11mm
3/8 - 9.5mm

Maybe the 'standard' sized rivnuts all need imperial holes drilling? Or just a coincidence...

That might well be the case.
I know I have some that are not the same o/d despite being the same thread. Some have thicker walls than others. I have a load of really odd size metric drill bits in the box as I do like MBB says and measure the o/d then go a couple of points up on the drill bit.
Never thought to see if they all match up to imperial sizes. I need to find a digital caliper that reads in 1/16th's

 

[Nick DV]

Just mic the outside dia of the rivnut and drill to a tight fit.

Absolutely Rivnuts seem to vary in size depending on where you get them from, so definitely get the rivnuts before you drill the holes.

 

[bigegg]

If i change suppliers or materials, I always find a bit of scrap of the correct thickness and do test fits (bore size and washers) to ensure correct fit - on pop rivets AND rivnuts.

Easier to check five or six variations on the bench than risk wrecking a job having to drill out.

I file the test pieces (or at least the results) in the tub with the rivets.