Every clamp, like the one shown, that I have seen will take a number 2. Do not twist the wires as they must be perfectly aligned to fit into the hole. It is a very tight fit.Hello
Do you always have to put the grounding wire through the screw in the clamp? Or can it connect to the pipe and the two outter most screws would hold it to the pipe via the clamp? #2 wire that has sheathing won’t fit through that small of a hole