Velect,
The holes are not marked for grounding, but in the situation I was referring to, the standard hole was unusable. It seems reasonable that it would be legal to drill and tap for a 10-32 ground screw. I just noticed that those holes in a 4" sq. box happen to be the right size thus eliminating the drilling step. Using a thread-cutting ground screw, such at a Dottie #1032TC, eliminates the tapping step. The holes in a 4 11/16" box are too big.
Now I suppose Don Rescapt will come along and question whether the holes provide for a 75% thread.
~Peter
