Counterbores

Part of speech: noun, verb

Definitions

1. Holes enlarged around a smaller hole to allow the head of a fastener to sit flush or below a surface; the process of creating such holes in a material; a tool used for making these enlarged holes designed to accommodate fastener heads
2. Enlargements made at the mouth of drilled holes to permit fastener heads to be recessed; the act of machining these stepped holes; implements employed to produce such recesses for screws or bolts
3. Circular recesses bored around pilot holes to fit bolt or screw heads flush with or beneath a surface; the procedure of forming these stepped openings; specialized cutting instruments used to accomplish the countersinking of fasteners

Etymology: "Counterbores" is the plural of "counterbore," a term for a stepped hole in which the top is widened so a screw or bolt head can sit below the surface. The word is a compound of "counter," from Latin "contrā" meaning "against," passed through Old French "contre" and Anglo-Norman "countre" into Middle English, and "bore," from Old English "borian," meaning to pierce or make a hole. Together they describe a bore made in opposition to, or on the opposite side of, an existing one. The verb and the tool share the same name, so a single term covers the act of machining these recesses and the cutter used to do it. The "counter" element carries its older sense of "against" or "opposite," the same idea found in words like "counteract" and "counterpart."

Synonyms: recesses, countersinks, drills