Countersunk

Countersunk describes a fastener head style and the matching tapered recess in the material that allows the head to sit flush with, or slightly below, the surface when installed. A common example is a flat head screw used in a countersunk hole: the conical underside of the screw head nests into the countersink so the top of the head doesn’t protrude. Countersunk fasteners are often specified when a smooth surface is needed for appearance, clearance, or to prevent snagging.

Countersunk features are also defined by an included angle, which must match between the screw head and the machined countersink for proper contact and load distribution. If the angles don’t match or the countersink is too deep or too shallow, the head may not seat correctly, reducing clamp load or damaging the surrounding material. Countersunk screws are common in sheet metal, panels, hinges, and hardware where flush mounting matters, but they can be less ideal in very soft materials unless the design includes enough bearing area or uses a compatible washer or insert to prevent pull-through.