Countersink

A countersink is a conical hole cut into a material so that the head of a flat-head screw, bolt, or rivet sits flush with or below the surrounding surface. The conical recess matches the angle of the fastener’s head — typically 82° or 90° in woodworking, or 90° in general metalwork — allowing the fastener to draw tight without protruding.

How it works

A countersink drill bit combines a pilot-bit tip with a conical cutter. The pilot guides the bit through the workpiece while the cutter enlarges the top of the hole into a cone. Once the screw is driven, its flat head nests into the cone and stops flush with the surface. This prevents snags, splinters, and visible hardware on finished work.

Why it matters

• Flush finish. Screws sit level with the surface, which is essential for furniture, cabinetry, and trim where protruding heads would be unsightly or catch on fabric and skin.
• Stronger joints. In plywood and veneered panels, countersinking cleanly cuts the top veneer layer, preventing splintering and tear-out.
• Safety. Eliminating protruding screw heads removes a snagging hazard on walking surfaces, door frames, and children’s furniture.

Countersink vs. counterbore

A counterbore creates a cylindrical recess so a socket-head cap screw or bolt can sit below the surface, often hidden by a plug. A countersink creates a cone; a counterbore creates a cylinder. The choice depends on the fastener head shape: flat heads need countersinks, socket heads need counterbores.

Related terms

• Pilot hole — the initial hole that guides the screw and prevents wood splitting.
• Dowel — a cylindrical pin used for alignment or reinforcement, sometimes paired with countersunk screws in mixed joinery.
• Plug — a wood cap glued over a counterbore to hide the fastener entirely.