A countersink is a conical-shaped hole that allows the head of a screw or bolt to sit flush with or below the surface of a material. This design helps to prevent snagging and provides a cleaner, more finished appearance. Countersinks are commonly used in woodworking, metalworking, and construction. To create a countersink, a special tool called a countersink bit is used, which can be attached to a drill. The size of the countersink must match the screw or bolt being used to ensure a proper fit. Properly countersinking can improve the strength and aesthetics of a project.