What does counterbored mean?
Counterbored describes a hole or machined feature containing a counterbore: a cylindrical recess cut into the opening of the hole so that a fastener head or other component can sit below the surrounding surface. The arrangement is useful when a flush or uninterrupted finish is wanted without the sloping profile associated with a countersunk fastener. As a verb, counterbored is the past tense and past participle of counterbore, meaning that such a recess was machined. The word occurs chiefly in engineering, manufacturing, metalworking, and woodworking, where the exact shape and depth of a recess may be important to the design. Although the terms counterbore and countersunk can sometimes be confused, they describe different geometries: a counterbore is cylindrical with a flat bottom, while a countersink is conical. Counterbored is therefore more immediately associated with a hidden socket-head fastener, though its use is not limited to bolts.
Having a counterbore, especially describing a hole with a flat-bottomed cylindrical recess at its opening.
"The plate has a counterbored hole for the recessed socket-head bolt."
Chiefly used in technical and manufacturing contexts.
The past tense and past participle of counterbore: to cut a cylindrical, flat-bottomed recess in a hole.
"The machinist counterbored the plate before fitting the bolt."
Usually used in a completed-action or participial construction, such as “counterbored the plate” or “the hole was counterbored.”
A counterbored hole lets a bolt head disappear below the surface; a countersunk hole makes it disappear at an angle.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does counterbored come from?
“Counterbored” is formed from the English compound “counterbore,” itself built from “counter-” and “bore,” the older word for drilling a hole. The compound developed within the technical vocabulary of machining, where a bore or counterbore is a cylindrical hole or recess. The adjectival and verbal participial form “counterbored” follows the usual English pattern of adding “-ed” to the verb “counterbore,” and it shares its terminology with related forms such as “counterboring” and “counterbores.”
How counterbored is actually used
This is specialist engineering and machining vocabulary, especially used in mechanical design, manufacturing, woodworking, and metalworking. As an adjective, it commonly follows the name of the object being described, as in “counterbored hole.” The verb normally takes a hole, workpiece, or other object as its object.
Easily confused with counterbored
A counterbore is the cylindrical recess itself, while counterbored describes a hole or other feature that has one.
A counterbored hole has a flat-bottomed cylindrical recess, whereas a countersunk hole has a conical recess shaped to receive a sloping fastener head.