Definition
A measuring tool with two curved legs that bow outward, used to measure the inside dimension of a hole, bore, or recess. The legs are adjusted until they just touch the inner walls of the opening, and the spread between the tips is then measured against a rule or micrometer to determine the dimension.
Plain English
A simple hand tool used to measure the width of a hole or opening from the inside. You spread the legs until they touch both inner walls, then measure the gap between the tip points to find the size.
Context Anchor
Seen in aircraft maintenance, inspection, and shop work when checking the inside size of openings, holes, tubes, or fitted parts.
Derivation
Caliper comes from an old form of the word 'caliber,' meaning the diameter or bore of something. 'Inside' specifies that this version measures inner dimensions, distinguishing it from outside calipers, which measure external dimensions.
Why Pilots Care
Precise internal measurements confirm that critical aircraft parts meet exact tolerances, preventing wear, vibration, or failure.
Intuition Check
Do not think of inside calipers as ordinary calipers used in an indoor location. Inside means the tool measures between inner surfaces, not across the outside of an object.
Example Sentence 1
The mechanic used inside calipers to check the bore of the engine cylinder for wear.
Example Sentence 2
After fitting the inside calipers to the piston pin hole, the technician transferred the reading to a micrometer for verification.