Daedalus454 said:
No, you are absolutely correct. In a "standard" installation, the clamping force is all that keeps a rivnut from spinning. As 5-90 and I mentioned, some sort of adhesive on the rivnut right before bucking can help alleviate this, but there is nothing as irritating as a spinning rivnut installed in a "blind" location with a seized fastener stuck in it.
Ayuh. Rivnuts are mainly so you can use machine screws or thumbscrews to retain access panels in sheetmetal construction. They're not meant for anything structural - that's what plate nuts are for.
Rivnuts have the advantage of installing a machine thread, which can make access panel removal easier (use a coarse machine thread for things you need to get to in a hurry - they come out faster, since they have a larger "lead" on the screw thread.)
If you want to "hurry" install in anything structural, you can use a "swage nut" - it's rather like a Rivnut, but it has collars on both sides, the collars lock together with a spline, and the mating surfaces with the panel have swage splines in them that help keep the thing from spinning (but they're still not great.) A plate nut is good, a weld nut is better, and just welding the damn thing together is best (structural joins typically don't require periodic disassembly.)
Rivnuts can be thought of as a heavy-duty version of a rubber well nut - but while well nuts are easy to install the first time, they're typically not reusable. They work well for parts that don't require a great deal of strength, or when vibration is a concern, or similar things (I use them for mount kits on my ANL fuse blocks, and will probably use them for more.)
Rivnuts are good for access panels, but if you want to get into the thing quickly, you're better using a Dzus - since a quarter-turn releases the thing fully. Dzus are available in a slotted head (use a quarter or something similar) for a flush appearance, or with "wings" like a wing nut for when appearance isn't an issue, and access is (the wings are typically large enough to grab with gloves on as well.)