A countersink is a conical hole cut into a workpiece, or the cutter used to cut it, most often made so the head of a countersunk screw, bolt or rivet can sit flush with or below the surrounding surface once driven home. Compared to a counterbore, which cuts a flat-bottomed hole for a socket-head fastener, a countersink's cone shape matches the underside of a flat or oval fastener head; it is also used simply to remove the sharp burr a drilling or tapping operation leaves behind.
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Introduced When (Circa)Not established by the cited source.
Countersink (Wikipedia) describes the tools geometry, types and machining use but gives no date or era for when the countersink was introduced; checked fresh 2026-09-17 against the raw article extract. OriginNot established by the cited source.
Countersink (Wikipedia) gives no origin story or inventor, only a technical description of the tools geometry and machining use; checked fresh 2026-09-17 against the raw article extract. Reader Challenges (0)
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