"Proctologically Violated©®"
was looking for a spring...

I'm not sure I've ever heard a specific name for that device except
"retainer spring" or "retainer clip".

It's nothing but a torsion spring with looped ends, and the coil sized
to fit snug on a certain size rod.

You can work backwards. McMaster lists their torsion springs by the
largest rod they can work on without interference. Their springs
don't have looped ends, but a pencil torch, needle-noses, and a quick
quench could solve that.

Pick one just a tad too small for the rod/tube/shaft you're working
with.

LLoyd