The final holes are 3/16" through these thick chunks of metal. I was drilling all the holes with 3/32" pilot holes and the drill bits kept binding in the metal when they got more than half way through. After drilling all the holes only part way through I went to the 5/32" and finally the 3/16" bits. What I discovered was the larger bits go through the aluminum really easy, so...
Best to just start the holes with 3/32", but don't go very deep. Otherwise it's a waste of time and it's frustrating. Then switch to the fatter bit(s) and they will cut through nearly like butter.
