The drill bit is a 3/4" masonry bit. That is the largest I could find that would fit in my 5/8" drill chuck. The OD of the 1/2" ID PVC is actually about 13/16", so I do a little wiggle with it when I drill. I have a short 10" piece of the pipe that I use to test it to make sure before I am done. The Figi-type live rocks are actually very easy to drill through, piece of cake, it is almost too easy and you have to be carefull where you strategically drill. The trick is to secure the rock so it doesn't spin, go slow with the pressure but use a high speed on the drill. I take it out of the tank, drill it in about 20 seconds, check the diamter with the test pipe, then rinse it in a bucket of tank water, and put it back all within about 2-3 minutes. I have a few pieces of Holey Rock, and that is certainly tougher to drill.