need more than one core for granite, best bet to get in a proffessional with a drill stand to do the job. granite will destroy a normal drilling system used by your average plumber, plus your arms will fall off before you get through the wall. How do I know, me house is built of stone and rubble with a brick facing, the walls are 24" thick and ive worn out numerous core drills and cores when i turned the building into flats, and ive arms like an orangutang now. I got in a man with a water cooled core drill in the end and it worked out cheaper than a drill and 4"core.