M3 size rivnuts can easily be inserted with a simple pop riveter (pop rivet gun) – it will take you longer to read this page than to actually do the job!
First observe your rivnut, see how the ribbed portion has no threads, this is the area which will compress behind the panel, see how little you have to “pull”.
Rivnuts come in different metals, I would recommend zinc plated carbon steel unless weight is an issue, then you can use aluminium. Stainless is also available but they may to be a problem to set using a pop riveter in this method.
Take a 40mm long (or longer, but no shorter) M3 screw.
Cut the head off it, and if you like grind a slot into one end, to make it like a really long grub screw (set screw).
Screw it into the rivnut so it just protrudes the back side. See how this assembly looks a lot like a pop rivet!
Take your pop riveter with probably the largest size nozzle, insert your assembled “rivet” into it.
If it doesn’t easily insert, make sure the nozzle is screwed in all the way, or go up a size (even if it fits in the hole, the nozzle might be just short enough not to work).
Insert the rivet into the hole you want to install it into and press the riveter tight against the surface like you would if you were about to insert a rivet.
Aluminium (Aluminum) Rivnuts: Very carefully squeeze the handles, not all the way just until the rivnut is suitably secure, not wobbly. If you squeeze all the way on an Aluminium rivnut you will easily rip the threads out of the nut!
Zinc Plated Steel Rivnuts: Just squeeze the handles all the way, you won’t be ripping the threads out of them.
Stainless Steel Rivnuts: These may not work, the rivet tends to be so hard that it actually bends the screw, and eventually said screw snaps in two. A very close fitting hole and thicker panel might help.
Now all that is left to do unscrew that headless screw, wiggle fingers, pliers, or that slot you cut into it with a flat bladed screwdriver. Job done!
Tie the headless screw to your rivet gun so you don’t lose it for next time.
Two perfectly riveted M3 rivnuts with no special tools (except a pop riveter).
Yes there are other no-tool methods, but this is way easier, faster and more reliable.
I highly recommend you drill a couple of practice holes in some sheet metal to get the feel of it, remember when using an Aluminium rivnut that if you just squeeze with the strength of the gods like you were doing a pop rivet you’ll rip the threads out, and it really will be like a pop rivet then, with a useless hole in the middle! Steel (zinc plated or stainless) won’t have that problem.