Drill a hole, insert one of these things, put a tool in it like a rivet gun, and pull the trigger. It installs a nut in places where you can't get behind to put a real nut.
I'm an old aircraft mechanic and I hate my ex-wife MUCH more than rivnuts!rivnuts....... even though they arent as great as what people think. Most the older aircraft mechanics I know hate them worse than their ex wifes.......
Floating nut plates are mucho better.........