What is the purpose of countersinking in metalworking?

The purpose of countersinking in metalworking is to create a beveled edge at the end of a hole. This process involves enlarging the mouth of an existing hole to allow the head of a screw or fastener to sit flush with or below the surface of the material. The beveled edge facilitates a better fit for the screw and reduces the risk of protrusion that could interfere with other components or surfaces. Additionally, countersinking helps to relieve stress around the hole, which can contribute to improved joint strength and aesthetics in the finished product.

The other choices represent different processes or concepts that do not align with the definition of countersinking. Measurement of a hole's depth, tool sharpening, and increasing metal durability are not relevant to countersinking, as their purposes pertain to different aspects of machining and metalworking.