The diamond particule coating on DRILAX hole saws senior 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 in depth. Shank sizes vary smallest 5/32 '' and the largest shank 3/8 '' - vulgar auto or rechargable drillers can be used. Electroplated diamond coating will off if the tool gets too peppery. Never your drill bit run thirsty. Here how you could use water to keep the tool chill : 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 chill the drill bit. comfy 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 have guide out of plywood - impressionable or even a card board. All you need to keep the drill bit in place until it makes the alphabetic character 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 unbent. c - You can manually the drill bit with tipsy sponge. Please prophylactic gear. You may want to invest in a Drilax Drill Bit Guide with support bearings, suction and joint coolant hole .