1. A flat-bottomed cylindrical enlargement of the mouth of a hole, usually of slight depth, as for receiving a cylindrical screw head.
2. A kind of pin drill with the cutting edge or edges normal to the axis; — used for enlarging a hole, or for forming a flat-bottomed recess at its mouth.
COUNTERBORE
Coun`ter*bore" (koun`tr-br"), v. t.
Defn: To form a counterbore in, by boring, turning, or drilling; to enlarge, as a hole, by means of a counterbore.
COUNTER BRACE
Coun"ter brace` (brs`).
1. (Naut.)
Defn: The brace of the fore-topsail on the leeward side of a vessel.
2. (Engin.)
Defn: A brace, in a framed structure, which resists a strain of a character opposite to that which a main brace is designed to receive.
Note: In a quadrilateral system of bracing, the main brace is usually in the direction of one diagonal, and the counter brace in the direction of the other. Strains in counter braces are occasioned by the live load only, as, in a roof, by the wind, or, in a bridge, by a moving train.