I think George Little is correct.
Look at the screws on devices, if he is wrong and any machine screw is suitable for grounding we could replace screws on devices with machine screws and claim code compliance. I think that is a violation of the devices listing.
This all comes down to whose opinion is regarded not who is right.
As an inspector or contractor I would make public what "proof" I would supply or accept. I guesss I would accept as proof I was wrong either the NEC code commentary or the ROCs. I would also accept a written statement (accepting liability) from a Licensed engineer.
Green screws or machine screws is not a big issue. You work small issues out and get on with your work. Being right is too expensive.
