The thickest wire I have used is the BJC 10 awg and it just fits into their own locking banana plugs. I doubt there would be many plugs compatible with that wire.
For the hell of it, I've tried running 10 awg bare and it is just a pita getting it into the binding posts on the back of the electronics. I can't imagine going 9 or lower.
I think it would be more of a detriment if you are stuck going bare with that thick of wire because you would be more prone to whiskers shutting down the electronics. Even with the 10 it's also tough getting a tight, secure connection (gets loose over time) going bare wire on the binding posts.
