ppl. a. and sb. [Pa. pple. of COUNTERSINK v.]
A. ppl. a. Said of a hole or cavity: Cut to receive the head of a bolt, screw, etc. Of a bolt, screw, etc.: Sunk or let in so as to lie flush with the surface.
1794. W. Felton, Carriages, Gloss., Counter Sunk Bolt, a bolt, the head of which is let in level with the surface of the plate it fixes.
1865. Tylor, Early Hist. Man., ix. 241–2. A piece of the same stone imbedded, with a countersunk cavity.
1884. Notes Building Constr. (Rivington), II. 357. Countersunk rivets are those in which the point is hammered down, while hot, flush with the surface of the plate.
B. sb. (See quots.); = COUNTERSINK sb. 2. Hence † Countersunk bit. Obs.
1794. Rigging & Seamanship, I. 151. Countersunk, a hollow, cut by a bit round the edge of a hole. Counter-sunk bit, a bit having two cutting edges at the end, reversed to each other, which form an angle from the point.
c. 1850. Rudim. Navig. (Weale), 112. Countersunk. The hollows in iron plates, &c. which are excavated by an instrument called a countersunk bitt, to receive the heads of screws or nails.
