My derailleur is hanging a little loose...the nut holding it to the hanger is like those on the backside of a chainring...So I need a really wide skinny screwdriver--which I don't have.

What might I have lying around that will do the trick? I'd rather not buy a special tool for this limited purpose.

TIA

A sacrificial butter knife? Better yet would be a spackle/joint compound knife. It's thicker so it won't leave a burr.

epoxy

A penny and a pair of pliers.

I'd just stake it with a centerpunch.

There should be a bolt that goes into that nut. It typically doubles as the main pivot for the RD. Most likely it's a 5mm allen-key that tightens the bolt.

Bolt side is fine...and, yes, it's a 5mm allen

It's the nut side that I'm having an issue with as hanger is not threaded...nut is similar to nuts on chainring.

CNW-2

It sounds like the hanger was repaired in the past by drilling out the original threads and adding a threaded insert.

As recommended, a putty knife or other wide piece of metal can be used as a holder to keep the insert from turning. Another possibility is to remove the derailleur, remove the insert and degrease the back of the hanger and shoulder of the insert. Then it may stay in place as you tighten the derailleur's attachment bolt.

All set!

The penny/pliers worked like a charm...

HillRider...no previous repair. This is an aluminum frame w/a replaceable hanger...working as designed.