Definition
A flat, ring-shaped piece of hardware placed between a fastener (such as a bolt head or nut) and the surface being clamped. Washers distribute the clamping load over a wider area, protect the surface from damage as the fastener is tightened, and in some forms help prevent the fastener from loosening in service.
Plain English
A small flat ring that goes under a bolt or nut. It spreads out the pressure when the bolt is tightened so the surface underneath doesn't get crushed or marked, and on aircraft it also helps the bolt stay tight.
Context Anchor
Seen in aircraft maintenance, preflight inspection findings, parts manuals, and hardware installation instructions.
Derivation
From the verb 'wash,' originally meaning to move or rub against. The name comes from the way the ring sits between two surfaces and takes the wear or movement that would otherwise occur between them.
Why Pilots Care
Vibration in flight can loosen bolts; the right washer helps keep critical fasteners tight and prevents metal fatigue or damage.
Intuition Check
Do not think of “washer” as a cleaning device here. In aircraft hardware, a washer is a small ring-shaped part used with a bolt, screw, or nut.
Example Sentence 1
The mechanic placed a flat washer under the bolt head before torquing it to the specified value.
Example Sentence 2
A lock washer was installed on the engine mount bolts to resist vibration loosening.