[Robin427]

I've got the pop rivet gun type (Spiralux Eclipse). You can buy cheap ones for about £20 (Laser) but mine cost about £60. I've used both steel and aluminium rivnuts (bought off eBay - do a search for "rivet nut" - about £3.50 for 50 M6). Mine came with M4,M5,M6 and M8 mandrels.

I do find that if you screw the rivnut fully on to the mandrel, the legs of the tool are too far apart to get a decent grip on. If you don't screw them in all the way you run the risk of stripping the threads.

My Landrover is currently 82% rivnuts. The Cobra is trailing but catching up...