What does "countersink" mean?

Countersink: To cause to sink even with or below the surface; as, to countersink a screw or bolt into woodwork.

Additional senses

  1. 2.An enlargement of the upper part of a hole, forming a cavity or depression for receiving the head of a screw or bolt. Note: In the United States a flaring cavity formed by chamfering the edges of a round hole is called a countersink, while a cylindrical flat-bottomed enlargement of the mouth of the hole is usually called a conterbore.
  2. 3.A drill or cutting tool for countersinking holes.

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