aren't you required to have a front plate in CA? you can only drill as small as the shafts of the rivets are, and I think they are about 1/4 inch. To drill the head of the rivet off, though, I think you will want to use a drill bit slightly larger than the hole in the head in the rivet. The rivets are very soft (possibly aluminum) and they spin when you try to drill them, which requires you to apply a moderate amount of pressure in order to get the bit to bite into them. out of 4, I went all the way through on one of the rivets, and let me tell you, that plastic is like butter. the one hole is not much bigger than the others, and with the plugs in, nobody will no except me (and now all of you).