How does countersinking prepare a hole for a screw?

Countersinking is a machining process that uses a specialized bit or drill to create a funnel-shaped enlargement at the outer end of a previously drilled hole.1

This preparation is essential for installing screws with tapered heads, such as flat-head screws. By creating this conical recess, the tool allows the screw head to sit flush with or below the surface of the material rather than protruding above it. This results in a smooth, finished appearance and prevents the screw head from snagging or interfering with other components.1