The diamond particule coating on DRILAX hole saws superlative performance and lifetime. Please our tools do not need center pilot holes. Center pilot hole drills are mostly for wood, , etc.. Drilax tools can 1 1/4 '' in depth. Shank sizes but the largest shank is 1/4 '' - standard galvanizing or rechargable drillers can be used. Electroplated diamond coating will off if the tool gets too sweltry. Never your drill bit run withered. Here how you could use water to keep the tool cool : a - You can build a mini water dam around the hole with plumbers putty. b - You can to spray water on the drill bit. c - Or you can running water to cool the drill bit. leisurely TO USE Center pilot drill bits are for wood, metal, etc. ; Here how you can keep the drill bit on target : a - You can make your ain guide out of plywood - moldable or even a card board. All you need to keep the drill bit in place until it makes the letter marks. b - You can drilling at an angle, with the edge of the drill bit making a C slot and then getting the drill bit up to erect . c - You can manually the drill bit with muggy sponge. Please guardian gear.