TORK CRAFT COUNTERSINK CARB.STEEL 5/8' (15.9 mm) T CS204Carbon Steel Countersink Countersink for Wood A countersink is a conical hole cut into a manufactured object. The same term is used for the cutter used to cut such a hole. Common uses: A common use is to allow the head of a countersunk bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material. A countersink may also be used to remove the burr left from a drilling or tapping operation thereby improving