Definition
A form of surface damage in which two metal parts under load slide against each other, causing localized welding, tearing, and transfer of material from one surface to the other. The result is roughened, scored, or seized surfaces that no longer move smoothly.
Plain English
When two metal parts rub together hard, tiny spots can briefly stick and tear pieces off one surface, leaving the metal scratched, rough, or jammed.
Context Anchor
Seen in aircraft maintenance when inspecting or assembling bolts, screws, hinges, fittings, and other metal parts that move against each other or are tightened together.
Derivation
From an older English use of 'gall' meaning to chafe or rub sore, originally describing skin worn raw by friction. The mechanical sense carries the same idea: surfaces damaged by rubbing under pressure.
Why Pilots Care
Galled parts can seize, bind, or fail. A galled bolt may snap during removal, a galled bearing can lock up, and galled control surface hardware can affect smooth operation. Recognizing galling helps technicians replace parts before failure and use anti-seize compounds correctly during assembly.
Analogy
It is like two rough surfaces grabbing each other instead of sliding; the more force you add, the more they tear at each other.
Intuition Check
Galling does not mean a part is merely irritating or difficult to move. In maintenance, it means real surface damage caused by metal rubbing, sticking, and tearing.
Example Sentence 1
The technician applied anti-seize compound to the stainless steel bolt threads to prevent galling during installation.
Example Sentence 2
After removal, the fitting showed light galling on the contact surfaces and had to be replaced.