Gordon wrote:You need a tool "rivet nut gun" to fit them, it collapses them into place much like a pop rivet...
Rivet nut tool kit (for reference, not price)
For the amount of torque they have to hold;
if one has gone loose, it would probably be worth working super-glue into the outer edge of the fitting, while spinning it to work the glue in.. let it cure for a bit and see if it bites..
super-glue is pretty good on close-fit metal-to-metal... after all, threadlock and bearing lock are basically the same thing
once secured, try running a tap down it to make sure the tread is clean, then use stainless setscrews/bolts in it to keep things clean for the future.
I've been using these for over 20-years; thought I was the only one! I like to use aluminium (threaded) inserts as they are far easier to compress (AL being a soft metal) than steel, which is a real bear to work with. I've even attached step-rails on trucks, a rear-spoiler, and even a tow-package (rear-hitch). The AL come in larger-sizes, 8 & 10mm, as you can still compress that size with your hands using the tool. Note that the 100% compression of the nut-sert is vital to the strength of the "hold". Also, the tighter you screw-in the bolt the more it pulls the threaded-insert towards it. You should functionally end up with only super-compressed soft-metal between your bolt & the steel-body of the car. ALWAYS use PLENTY of long-lasting SYNTHETIC lube in the threads of the nut-sert, as that way you can easily remove the bolt years later.
Note that the centre-section of the insert collapses around the inside-layer it is being pulled towards, affording a large radial-surface to spread the load over. Therefore, it provides a far stronger bond than a sheet-metal screw.
