walrus,
I agree that it appears that the panel member was asking for a green screw, but "identified for the purpose" is another murky area of the code.
Identified (as applied to equipment). Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.
FPN: Some examples of ways to determine suitability of equipment for a specific purpose, environment, or application include investigations by a qualified testing laboratory (listing and labeling), an inspection agency, or other organizations concerned with product evaluation.
It does not come right out and require a listed product, but only says in the FPN that a listing is one way to "identity for the purpose".
I still see no electrical reason why a standard machine screw cannot be used in any threaded hole in the box for the termination of the EGC. I'd be willing to bet that if you used a micro-ohm meter that any type of machine screw would show less connection resistance than the listed push-on clamp device and that there would no difference in the readings between the green screw, the cpamp screw or a hardware store machine screw.
Don
