Definition
A precision measuring instrument with a fixed jaw and a sliding jaw mounted on a graduated scale, used to measure outside dimensions, inside dimensions, and depths of mechanical parts. The reading is taken from the main scale together with a vernier or dial scale that allows fractional measurements smaller than the smallest main-scale division.
Plain English
A measuring tool with two jaws — one fixed, one that slides — used to accurately measure how thick, wide, or deep a part is.
Context Anchor
Seen in aviation maintenance when checking whether a part matches the required size before it is installed or returned to service.
Derivation
‘Caliper’ comes from the older word ‘caliber,’ meaning the diameter or size of something. ‘Slide’ refers to the moving jaw that runs along the scale. So a slide caliper is literally a sliding-jaw size-measurer.
Why Pilots Care
Aircraft tolerances are tight. A slide caliper lets a technician confirm a part is within service limits before it goes back on the aircraft.
Intuition Check
Do not think of a slide caliper as a clamp. It may grip a part lightly while measuring, but its job is to measure size, not hold the part in place.
Example Sentence 1
The technician used a slide caliper to measure the diameter of the bolt before ordering a replacement.
Example Sentence 2
Check the thickness of the new washer with a slide caliper to ensure it meets specifications.