What does countersink mean?
A countersink is a cone-shaped recess cut into the surface of a material around the entrance of a drilled hole, designed to let a flat-headed screw or rivet sit flush with—or just below—the surrounding surface. The word also names the specialized fluted cutting tool used to create that recess, and it functions as a verb meaning to cut such a recess. Countersinking is routine practice in carpentry, cabinetry, metal fabrication, and engineering wherever protruding fastener heads would be unsightly, hazardous, or mechanically problematic. It should not be confused with a counterbore, which cuts a straight-sided cylindrical pocket rather than a tapered one. In everyday use the word belongs chiefly to trade and do-it-yourself contexts, and the related form 'countersunk' describes screws manufactured with heads shaped to fit these recesses. Simple in concept yet indispensable, the countersink exemplifies how a small geometric detail underpins clean, strong, professional joinery across countless everyday objects.
A conical recess cut around the mouth of a hole so that a flat-headed screw or rivet can sit flush with the surface; also, the fluted cutting tool used to make such a recess.
"He widened the top of each hole with a countersink before driving the screws home."
In workshop use the noun often refers specifically to the tool (the countersink bit), with context making clear which sense is meant.
To cut a conical recess at the surface of a hole so that a fastener head can lie flush with the surrounding material.
"Countersink each screw slightly below the surface, then fill the holes before painting."
The past participle 'countersunk' is standard in descriptions of hardware, as in 'countersunk screws'.
Standard plural, referring either to multiple recesses or multiple countersink tools.
"All the countersinks on the bracket were machined to the same angle."
That neat conical dip hiding every screw head on your furniture has its own name, its own drill bit, and a past stretching back to the age of hand woodworking.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of countersink
Countersink combines 'counter-', from Latin 'contra' meaning 'against' or 'opposite', with 'sink', from Old English 'sincan', meaning to descend or subside. The compound arose in English in the late 17th century as a technical term in woodworking and metalworking, describing a recess sunk counter to, or opposite to, the main bore. Its components connect it etymologically to words like 'encounter' and 'contrary' through the shared Latin root 'contra'.
Related word forms
How countersink is actually used
Most common in carpentry, metalworking, and engineering contexts; the verb form is standard in trade and DIY writing. The adjective form of the verb's participle is 'countersunk' (e.g., 'a countersunk screw'), not 'countersinked'.
Easily confused with countersink
A counterbore is a cylindrical recess that lets a bolt head sit below the surface, while a countersink is a cone-shaped recess sized to a flat-head screw's taper.