Definition
A thin piece of material — typically metal, plastic, or laminated stock — placed between two parts to fill a gap, adjust spacing, or correct alignment. Shims are used to bring components into proper fit, level, or position when manufacturing tolerances or wear leave a small dimensional difference that must be made up.
Plain English
A thin spacer slipped between two parts to take up a small gap or to adjust how the parts line up.
Context Anchor
Seen in aircraft maintenance instructions, parts manuals, and logbook entries when a part needs a small spacing or alignment adjustment.
Derivation
From an 18th-century term for a thin slip or wedge of wood or metal inserted to fill space; the origin highlights its function as an adjustable filler rather than a structural part.
Why Pilots Care
Correct shimming prevents vibration, binding, or uneven wear that can lead to control problems or component failure.
Analogy
Like folding a piece of cardboard under one leg of a wobbly table to level it — same idea, just done with precision-cut metal.
Intuition Check
Do not think of a shim as a makeshift patch. In aircraft maintenance, a shim is an intentional spacer used to make a part fit or line up correctly.
Example Sentence 1
The mechanic added a thin shim behind the magneto mounting flange to correct the gear backlash.
Example Sentence 2
During the annual inspection, the mechanic checked the elevator hinge for missing shims that could cause play in the controls.