You can drill the center post with a 5/32" bit, then the small airflow holes around the hex section with 1/16". I would recommend only drilling half of the hex ones, if you do all the center post will become weak. If you go any larger on the center post without a drill press, you may damage the whole thing. I would recommend getting a cheap S4 Kit, as it makes it so much easier and not worth the extra effort of drilling.