Cut counter sink screw slots up to 1" deep for common #10 & #12 wood screws. A countersink is used when the fastener's head is conical in shape as in the case of a typical wood screw where the screw head needs to be flush or sit below the surface of the work piece. Alternatively, a counter bore hole is typically used when the fastener's head, such as a round head screw, is required to sit flush with or below the level of a work piece's surface. Our bits are constructed with a single solid carbide tip with virtually no centre web resulting in a very high-quality tool.