What is the preferred angle for countersinking holes in metal?

The preferred angle for countersinking holes in metal is 118 degrees. This angle is specifically chosen because it allows for optimal engagement with the heads of standard screws, which are designed to mate with this countersink angle. Using a 118-degree countersink facilitates proper seating of the screw, ensuring a secure fit that helps distribute loads evenly across the material.

Additionally, the 118-degree angle is common in the aircraft industry, particularly for aluminum alloys and many other metals, providing a balance between mechanical strength and ease of machining. This consistency enhances the reliability of structural components, as it accommodates a variety of fasteners while promoting effective load transfer in assembled structures.

Other angles, while they may have their specific applications, do not provide the same level of compatibility with the most frequently used fasteners in metalwork, especially in aviation.