counterbore

[ koun-ter-bawr, -bohr; koun-ter-bawr, -bohr ]

noun

1. a tool for enlarging a drilled hole for a portion of its length, as to permit sinking a screw head.
2. the portion of the hole so enlarged.

verb (used with object)

, coun·ter·bored, coun·ter·bor·ing.

1. to enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.

Other Words From

• counter·borer noun

Word History and Origins

Origin of counterbore¹

First recorded in 1605–15; counter- + bore ²

Example Sentences

For enlarging a hole for a certain distance the counterbore is employed.

From Project Gutenberg

A counterbore in the arbor hub provides clearance for the hub of the pulley which projects beyond the rim on one side.

From Project Gutenberg

If taken off at all it must be pulled, for the dowel-pins, key and counterbore are close fits.

From Project Gutenberg

When the cannon is loaded, a small quantity of powder is placed in the counterbore, and the spark between C and E ignites this and discharges the cannon.

From Project Gutenberg

For counterboring small holes or for facing the metal around their ends, the form of counterbore shown in Fig.

From Project Gutenberg