CB counterbores for recessing bolt and screw heads. Comes with a HSS slow spiral drill bit. Completely adjustable with supplied hex key. TCT version available for plywood, particle boards and plastics (abrasive). Use at drilling speeds only. Not suitable metals. When setting-up, make sure flutes of drill are aligned with flute of counterbore. For replacement Twist Drills, use slow spiral type e.g. 501/532 to 501/012.