What did you plug your fender antenna hole with?

Looking for some kind of plug ideas to plug the fender antenna hole with. 67 Barracuda.

Either a rubber grommet or a sink stopper have entered my mind, but if someone has any better ideas please list them. yeah, I know shoulda done it with the body work, but it was an after the fact decision.

No radio for me, gave my antenna mast away to a young gun.