I just found out today what a "rivet nut" is. If you have never seen one, they're an ingenious simple little jigger. You drill a hole in the frame, insert the rivet nut with the tool and viola you've got a threaded hole. The previous owner of my bike mounted the pannier rack using them. One's stripped out and I gotta replace it. Apparently they're also called 'Nutserts' and you can buy a complete kit including the fitting tool at engineering supply stores.