[机] 钻锥坑

Countersink \Coun"ter*sink`\ (koun"t[~e]r*s[i^][ng]k`; 277), v.
t. [imp. & p. p. {Countersunk} (-s[u^][ng]k`); p. pr. & vb.
n. {Countersinking}.]
1. To chamfer or form a depression around the top of (a hole
in wood, metal, etc.) for the reception of the head of a
screw or bolt below the surface, either wholly or in part;
as, to countersink a hole for a screw.

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