Like it says, I would like to be sure that I buy the proper size Rivnuts to affix the rubber backed aluminum brackets I fabricated to hold my windshield in place on the race car in the event of an impact. The metal of the windshield surround and of the cowl seem to be quite thin, and the Rivnuts I'm seeing appear to possibly be too deep to hold the Rivnut tightly in place. Anybody used Rivnuts for such an application, and if so, what size/dimensions did you use that worked well. Thanks, Mike.

Where are you putting them? Are these the bent metal tabs, like 2-3 along the bottom of the windshield and 2 more at the top? I've seen 6 mm and 1/4" bolts used for those. I use through bolts where I can. Are you putting tabs along A pillar as well? Is that why you want to use rivnuts? I guess with a removable roof you might need to do it that way. If you do the rivnuts, get steel ones. I'd worry about aluminum ones pulling out.

Are you using a polycarbonate windshield?

Note that SCCA no longer requires windshield clips or straps when you're using the OE-style bonded windshield. Many orgs follow/mirror/reference SCCA regs.

That said, 6mm or 1/4" rivnuts are more than sufficient to hold in a polycarbonate windshield.

Instead of removable fasteners I use 3 rivets on each bracket.

Chris beat me to it.
Or, alternately, if you have a need or desire to be able to remove them often and want to use rivnuts you could rivet small reinforcement plates using backing washers on the rivets, then Rivnut to them. I used this method at the attachment points on my fiberglass front and rear lids that use Camloc fasteners.

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Sorry for the slow reply. I'm using a stock glass windshield, bonded in place as standard. When getting the car through annual tach inspection with my local Vintage club, the Inspector questioned why I did not have windshield retaining brackets, and said that although not specifically required by the club, they were recommended. I seem to recall him to say that SCCA required them, but that might not be the case. Here's what I was planning on installing using the rivnuts.
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I would use M4 or M5.

Windshield clips are no longer required in SCCA for cars with factory bonded windshields; I had that reg changed in Fall 2019 (Production category).

It was not been required for other categories for vehicles with stock, bonded windshields, only those with rubber-lip-secured windshields and those that could replace theirs with polycarb.

Its existence in Production was a leftover vestige from the days back before windshields were bonded (and our scarves flowed in the wind down the straights). Its 2019 regs change was a result of an over-zelous Tech inspector - someone from the flowing-scarves days - who decided to do a paddock "gotcha" on all the more-modern cars the week of the 2019 Runoffs, thus forcing many of us head over Home Depot and buy some strip aluminum and secure it around our windshields with zip screws (boy howdy did that increase our safety!) The CRB quickly adjusted the requirement after I sent in a "derp" letter.

Think about it from purely an engineering standpoint. The clips are there to retain your windshield from departing the car in case of an incident. If your windshield is bonded to the frame all the way around, what's a half-dozen clips lightly resting against that heavy windshield and held in with small screws going to do...?

It certainly doesn't hurt to do it if you want to, but it will offer no safety value. But check the regs of all the other groups you may choose to run with.

GA

FWIW mine are riveted similar to Chris F's with (3) large-head rivets each. Next time the windshield is out I may replace those with rivnuts though, cuz based on history I figure the windshield will be out yet again not long after that...