[f. next.]
1. A tool for countersinking: see the verb.
1816. J. Smith, Panorama Sci. & Art, I. 115. The head of the countersink is conical.
1849. Weale, Dict. Terms, 124. Countersinks for iron have two cutting edges forming an obtuse angle.
2. The conical enlargement of the upper part of a hole for receiving the head of a screw or bolt. Cf. COUNTERSUNK sb. Hence countersink bit, a bit for cutting a countersink.
1846. Worcester cites Tanner.
1869. Sir E. J. Reed, Shipbuild., xvii. 330. The shank is conically shaped under the head in order to fit the countersink.
1879. Cassell’s Techn. Educ., IV. 135/2. Punching … has … the advantage of giving a slight countersink, or conical form to the hole.
