1Pcs Hexagonal Shank Sinker Drills8mm 2.8-4.0mm conical sizedrilling and opening tools for screws

Premium Tungsten Carbide Wood Countersink Drill Bit with Hex Shank for Faster and Cleaner Holes Drilling A countersink is a conical hole cut into a manufactured object; a countersink bit (sometimes called simply countersink) is the cutter used to cut such a hole. A common use is to allow the head of a bolt or screw, with a shape exactly matching the countersunk hole, to sit flush with or below the surface of the surrounding material. (By comparison, a counterbore makes a flat-bottomed hole that might be used with a hex-headed capscrew.) A countersink may also be used to remove the burr left from a drilling or tapping operation.