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

That it may always do this and yet leave sufficient clearance, the counterbore has been devised.

From Project Gutenberg

The jaw end is counterbored out with a 45-degree counterbore to form a bearing for the forward end of the micrometer screw.

From Project Gutenberg

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

For counterboring small holes or for facing the metal around their ends, the form of counterbore shown in Fig. 1746 is employed.

From Project Gutenberg