Definition

1. Noun:
   • A type of drill bit or cutting tool: A counterbore is a cylindrical flat-bottomed tool used to enlarge the opening of an existing hole to a specific diameter and depth, typically to allow the head of a fastener (like a bolt or screw) to sit flush with or below the surface of the material.

Usage

• A counterbore is used in machining and metalworking to create a recess for a bolt head or nut.
• It is distinct from a countersink, which creates a conical recess.

Examples

• Noun:
  • The machinist used a counterbore to prepare the hole for the socket head cap screw.
  • Select the correct counterbore size to match the diameter of the fastener head.

Advanced Usage

• "To counterbore a hole" (verb form derived from noun): The act of using a counterbore tool.
  • You need to counterbore this hole before installing the bolt.

Variants and Related Words

• Counterboring (n/gerund): The machining operation performed with a counterbore.
  • Counterboring is a common step in assembly.
• Counterbored (adj): Describing a hole that has been processed with a counterbore.
  • The counterbored surface provides a clean finish.

Synonyms

• Spotface: A very shallow counterbore, often just to create a flat bearing surface.
• Boring tool: A more general term for tools that enlarge holes.

Related Terms (Not Phrasal Verbs)

• Countersink: A tool for making a conical recess, often confused with but functionally different from a counterbore.
• Drill bit: A cutting tool used to create cylindrical holes.

Noun

1. a bit for enlarging the upper part of a hole