Definitions

1. noun

A cutting tool, typically used in drilling machines, that makes a hole larger than the tool itself by removing material from the edges of the hole, typically used to create a larger diameter hole, such as for a bolt or nut.

“The engineer used a counterborer to enlarge the hole in the metal plate to accommodate the large nut.”

2. verb

To make a hole larger by removing material from the edges of the hole, typically with a counterborer.

“The machinist counterbored the hole to fit the bolt head.”