Definition

1. Noun:

   • A conical hole: A "countersink" is a conical-shaped hole drilled or milled into a material, typically wood or metal, which allows the head of a screw or bolt to sit flush with or below the surface.
   • A type of drill bit: A "countersink" is also a tool, specifically a drill bit, designed to create such a conical hole.

2. Verb:

   • To create a conical recess: To "countersink" means to drill or cut a conical hole so that a fastener's head will be level with or below the material's surface.
   • To set a fastener flush: To "countersink" also means to insert a screw, bolt, or nail into such a hole so its head does not protrude.

Usage Examples

• Noun (Tool):

  • I need a 90-degree countersink to prepare this hole for the screw.
  • The carpenter selected a countersink from his toolbox.

• Noun (Hole):

  • The screw head fits perfectly into the countersink.
  • Make sure the countersink is deep enough for the bolt head.

• Verb:

  • You must countersink the hole before driving the screw.
  • The instructions say to countersink all the screws for a smooth finish.

Advanced Usage

• Countersinking for rivets: The process is also used in metalworking for rivets, not just screws.

  • The aircraft skin requires each rivet hole to be countersunk.

• Countersink angle: Often specified by the included angle (e.g., 82°, 90°, 100°).

  • A 90-degree countersink is standard for flat-head screws.

Variants and Related Words

• Countersunk (Adjective/Verb Past Participle): Describes a fastener that has been set into a countersink.

  • The screws were neatly countersunk and filled with wood putty.

• Counterbore (Noun/Verb): A related but distinct process that creates a cylindrical flat-bottomed hole to seat a bolt head or nut. A counterbore is different from a countersink.

  • A counterbore is used when a socket-head cap screw needs to sit below the surface.

Synonyms

• Recess (Verb/Noun): To set into a hollow or to the hollow itself.
• Flush-set (Verb/Adjective): To set level with the surface.

Related Phrases

• To be countersunk: The passive form describing the state of the fastener.

  • All the fasteners on this deck are countersunk for safety.

• Countersink bit/drill: A common compound term for the tool.

  • He bought a new set of countersink bits for his project.

Noun

1. a bit for enlarging the upper part of a hole
2. a hole (usually in wood) with the top part enlarged so that a screw or bolt will fit into it and lie below the surface

Verb

1. insert (a nail or screw below the surface, as into a countersink)