The bottle mount rivnuts in my bike spun themselves loose years ago and I had just accepted that was how it was going to be. Until I learned that in recent Amazon donations, VHS received not one but actually like 5 rivnut setting tools, and mandrels for all the most common bolt sizes.
Once I drilled the heads of the old spinny rivnuts I could poke them with a screwdriver and hammer until they fell inside the frame:
The ones in the seat tube were easy to get out (remove seat, tip frame over), but the ones in the downtube required removing the fork which took a bit more faffing. 4 pieces went in, so I made sure I got 4 out.
New rivnuts installed. Yay! They don’t match the curvature of the tube perfectly like the originals did but they feel solid. Time will tell how good of a job I did. Yay, hydration!
p.s. We now have a set of stainless steel metric riv nuts.
p.p.s. If rivnuts are only a little bit loose it might be possible to use the tool to re-set them without completely replacing them, but these ones were super old and I didn’t trust them.