Uninsulated bare copper wire for turntable ground OK?

I have to span about 3 feet from TT to phono stage so the ground wire that the TT came with is too short. I have access to bare copper wiring that is long enough.  Is it fine to use this?

Add bare wire, you could try it, it cannot hurt anything. You could wrap it with tape as a quick solution if hum appears.

Some TT's don't have separate grounds. If it sounds good without the ground, as it might, ...

Are you concerned about keeping OEM appearance? IOW, remove your extension at some future time?

I have had to extend TT ground wires.  Just find/buy a length of insulated wire similar gauge, and use an insulated bullet type connector, easily found at Home Depot, 

It's not carrying a signal, just preventing hum, any quality that works is good enough

No problem using bare wire for that application!

Bare copper is the most commonly used type of copper wire and is often referred to with the general term “grounding wire.” It does not have any sort of protective coating, however, the lack of insulation allows bare copper to have the best conductive properties.
Perfectly OK to use bare wire for ground. Thick gauge best. But I don’t see any reason why it’s better than insulated wire of the same gauge and composition. Nor should the dielectric make any difference.  If I have some heavy gauge 3-wire Romex cable lying around, I like to strip out the bare ground wire and use it as ground wire in components.  You can get 12- or 14-gauge Romex at any good hardware store.
I put a 20 gauge OCC banana extension on mine. It is perfect. Tell me I’m wrong.
Yep.  It's fine.

You need insulated grounds for safety grounds (which this is not), but if it contacts any other metal which could have a potential it could put a lot of noise into your phono. I'd suggest you pick up any cheap hook up wire from Parts Express or the like.
Thanks all!.  My maintenance personal had bare copper wire at my business so it would be convenient.  I just wanted to avoid indoor stores (hardware) as I am in Los Angeles where COVID is raging.  Turns out, I needed to buy a door knob for my wife's closet today so I got insulated primary copper wire (solid core, 14g) and a set of spade terminators.