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COUNTERBORES Technical Information

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Basics of...Counterbores
Solid Pilot Counterbore for Fillister HeadScrews

Counterbores are used to enlarge a portion of an existing hole to hide the head of a screw or to provide a seat for a nut. They come with solid or interchangeable pilots, and many are built for making holes for a specific type of fastener.


Solid Pilot

  • Manufactured with the pilot attached to the cutting end of the tool
  • Provide a very accurate hole

Interchangeable Pilot

  • Do not come with an attached pilot
  • Separate pilot is attached by sliding the shank through a pilot-hole built into the counterbore
  • Better flexibility, as a single tool can be used in many different hole diameters by switching the pilot

Use a Counterbore for:

  • Socket head cap screws
  • Machine screws
  • Fillister head screws
  • Spot facing