The size of the hole will vary based on the anchor being used. Using a hammer drill, drill a hole in the base material the same diameter as the Kwik-bolt being used. The depth of the hole must be a minimum of one anchor diameter deeper than the embedment of the anchor. For example if you are using a 1/2" by 5.25" anchor, you would drill 1/2" deeper than the 3.35" from the base of the wedge to the collar equaling 3.85" total depth. - See more here.