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It was Poisson's ratio.
But more to the point ..
I think we're talking at crossed purposes here.
The items in question are solid metal threaded inserts, not composite rubber and brass..... yes ?
These are called rivnuts, not wellnuts.
And yes, you are supposed to fit them using a dedicated, special tool which kinda crimps them in place although it is possible to fit them using a nut and draw-bolt arrangement .. have a look on youtube.
If the old one is spinning, you'll need to fix it somehow before drilling it out.
The best way to do this would probably be by re-crimping it ... in which case once its solid you may not need to change it after all.
Another way might be to "stake" it with a centrepunch, but re-crimping makes more sense.
Or you may be able to grab it from inside with long nosed pliers to hold it while you drill, but that's probably a long shot.
If you do decide to remove it, you'll need an accurately sized drill in order to cut through the rivnut without damaging the hole that its in .. otherwise the new one won't tighten up when you fit it.
Although the rivnut will tolerate a small variation in hole size .. it'll just need crimping a bit further if you haven't gone too much bigger with the drill.
If you do replace it, you might as well fit a stainless one rather than a plain, plated steel one.
Oh, and I've just remembered, there are two types of rivnut .. one with a flanged head and the other with a countersunk head.
I believe you want the latter (so it lies flush with the surface when fitted) but remove the old one and have a look before ordering.
Final option, I have a spare steel swingarm from a yr2000 750, since I fitted an ally swinger to mine.
Might be more economical to use that instead of buying the rivnut crimping tool etc (its going cheap if you're interested and I'm just down the road in Leicester).
Its in good nick but needs new paint.
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