What size ground nut or ground screw is needed to ground gable-mount electric power fan Model WCGA?

The WCGA has a ground screw mounted in the thermostat housing, so no ground nut should be required.

The WCGA has a ground screw mounted in the thermostat housing, so no ground nut should be required. The screw is bright green and has a castellated nut allowing for the wire to have a recess to be fastened to the case. The ground wire fastened to this screw is subsequently fastened inside the power supply junction box with a wire nut or ground screw.