Bolting items to frame

[BrewBeemer]

I thought you were talking about standard hexagonal nuts and welding them to the frame.

NO! I said broached as this is what the hexagon nut does when seated into a round hole making the hole hexagoned.
A Hexnut will not spin out vs a Rivnut even when the Rivnut's installed with the correct pilot hole diameter. I can't explain it simpler. Dealing with both types myself many times I have nothing to do with Rivnuts, always had my shop order Hexnuts only. If Riv-nuts work for you go for it, I prefer Hexnuts with anti-seize on the bolt threads for easy future bolt removals.