Definition
A precision measuring tool consisting of a set of thin metal blades, each ground to an exact thickness, used to measure the size of small gaps or clearances between two parts. The blades are marked with their thickness in thousandths of an inch or in millimeters, and one or more blades are inserted into the gap until a snug fit is found, indicating the gap's dimension.
Plain English
A small fan-shaped tool made of thin metal strips of known thicknesses. You slide a strip into a gap, and when you find the strip that fits snugly, you read its label to learn how wide the gap is.
Context Anchor
Seen in aircraft maintenance, inspections, and repair work when a mechanic must confirm that a part or gap is within the allowed size.
Derivation
Also known as a feeler gauge. 'Feeler' describes how it's used: the thin blade 'feels' its way into the gap. 'Thickness' refers to what's actually being read — the thickness of the blade that fits.
Why Pilots Care
Confirms that critical airframe components remain above minimum thickness limits so the structure stays strong and safe.
Intuition Check
Do not think of a thickness gauge as a cockpit gauge on the instrument panel. In this context, it is a maintenance measuring tool used on parts or small gaps.
Example Sentence 1
The mechanic used a thickness gauge to check the spark plug gap before reinstalling it.
Example Sentence 2
After the patch was installed, the inspector verified its thickness with a gauge before signing off the repair.