countersink

[COUNTERSINK, v.] Mechanics: 1. An enlargement of a hole to receive the head of a screw or bolt. 2. A tool for making a countersink depre ion. Countersinks for wood have one cutter in the conic surface, and have the cutting edge more remote from the axis of the cone than any other part of the surface. Countersinks for bra have eleven or twelve cutters round the conic surface, so that the horizontal section represents a circular saw. These are called rose-countersinks. The conic angle at the vertex is about 90°. Countersinks for iron have two cutting edges, forming an obtuse angle. ( Weale.)