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Rivet nuts and I have had a checkered past. Sometimes they work great, and other times not so much. As far as I can tell, the biggest factor is having a tool that properly crimps them. Also, having good rivnuts helps too. I got this tool from Amazon. It's called Astro Pneumatic Tool 1427. Right now it's $35. It was well reviewed so I thought I'd give it a shot. I've used a plier-type before and they are terrible. I've also used an air-powered one and that was great. But this is a really good value. It comes with mandrels for M5, 6, 8, 10 and 12. The size is just right too, about a foot long so you have good leverage. But not so long that it's unwieldy or that you can't fit it into a lot of places.



I also got some nice zinc-coated knurled rivet nuts from McMaster. Part number 95105A175. They have a 0.5 to 3.3 grip range which is perfect for flat sheet metal, but my chassis has round tube, and they have just enough grip for that. The higher grip range might be better for the round tube. But I've installed a bunch so far in both flat and round and they seem to be holding well.

First test piece. Installed in thin (maybe .050") sheet


Backside


Rivnuts for level sender in fuel tank

I've had good luck with the knurled rivnuts and the rivnut tool from McMaster Carr. You have to keep everything flush to get the rivnut seated flat. I generally clamp down on it with the tool, screw in the head to bottom it out again and finish the crimp. Great hand exercise. I rivnutted all over my buggy. That sounds wrong. Most of the rivnuts are in .120 wall 1.25" square tube.

I'm glad that plier-type is working for you. They're a lot more versatile because you can get them in so many more places than the kind I have.

You can also get them with splines down the sides which helps insure they won't spin sometime later.

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I called it "knurled" but I think we're talking about the same thing. The one on the right is the McMaster one. The ribs down the side are definitely better than ribs under the head.

I'm sure your tool makes it easier. I do have a lot of rivnuts in odd places, so the pliers do ok. When my arthritis acts up, I don't use the pliers without some pain, though. I also bought all knurled rivnuts from McMaster.com. I had some rivnuts where I was bottoming socket head shoulder bolts. Every now and again the rivnuts would crimp with the threads off center of the drilled hole. On tight fitting shoulder bolts that was a problem.