counterbore: meaning, definition, pronunciation and examples
LowTechnical/Engineering
Quick answer
What does “counterbore” mean?
A cylindrical flat-bottomed enlargement of a drilled hole, designed to allow a screw or bolt head to sit flush with or below a surface.
Audio
Pronunciation
Definition
Meaning and Definition
A cylindrical flat-bottomed enlargement of a drilled hole, designed to allow a screw or bolt head to sit flush with or below a surface.
The cutting tool used to create such an enlarged hole; the machining operation of creating this feature; to perform this machining operation (verb).
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning or usage. Spelling and pronunciation are consistent. The process and tools are identical in both engineering traditions.
Connotations
Neutral technical term in both varieties.
Frequency
Equally low-frequency and confined to technical domains in both the UK and US.
Grammar
How to Use “counterbore” in a Sentence
[Subject] + counterbore + [Direct Object (e.g., the hole, the plate)][Direct Object (e.g., The hole)] + be + counterbored + [optional: to a depth of X]Vocabulary
Collocations
Examples
Examples of “counterbore” in a Sentence
verb
British English
- We need to counterbore this plate to a depth of 5mm.
- The technician will counterbore the hole for the bolt.
American English
- The drawing calls for us to counterbore this flange.
- Make sure you counterbore before tapping the threads.
Usage
Meaning in Context
Business
Rarely used outside of procurement or technical specifications, e.g., 'The part requires a counterbore for the mounting bolt.'
Academic
Used in engineering, manufacturing, and materials science texts and lectures.
Everyday
Virtually never used in non-technical conversation.
Technical
The primary domain. Common in mechanical drawings, machining manuals, CNC programming, and workshop discussions.
Watch out
Common Mistakes When Using “counterbore”
- Confusing it with 'countersink' (which has angled sides).
- Using it as a general term for any hole enlargement.
- Incorrect spelling as 'counter bore' (as two words is less standard in technical noun form).
FAQ
Frequently Asked Questions
No. A countersink creates a conical recess for a flat-head screw. A counterbore creates a cylindrical, flat-bottomed recess for a bolt head or nut, often to sit flush or below the surface.
Yes. For example: 'You need to counterbore this hole to a depth of 6mm.'
It is most common in mechanical engineering, machining, metalworking, woodworking (for certain fittings), and manufacturing.
A counterbore is created using a cutting tool called a counterbore cutter or an end mill with a pilot, which is a drill bit-like tool with a wider, flat-cutting end.
A cylindrical flat-bottomed enlargement of a drilled hole, designed to allow a screw or bolt head to sit flush with or below a surface.
Counterbore is usually technical/engineering in register.
Counterbore: in British English it is pronounced /ˈkaʊntəbɔː/, and in American English it is pronounced /ˈkaʊn(t)ərbɔːr/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “None”
Learning
Memory Aids
Mnemonic
Think: 'COUNTER' (against) + 'BORE' (to drill). You drill a hole, then you drill AGAIN, making a wider BORE to counter-sink (or rather, counter-flush) the fastener head.
Conceptual Metaphor
CREATING A NEST or POCKET: The counterbore is conceptualized as a prepared space or pocket that neatly houses and conceals a fastener's head.
Practice
Quiz
What is the primary purpose of a counterbore?