Glossary
flat washer
A flat washer is a thin disc that sits under a nut or bolt head and spreads the fastener's load over a wider area, so the surface is not crushed and the hole is not enlarged.
A flat washer is a thin metal disc with a hole in the middle, placed under a nut, a bolt head or a screw head. Its job is AREA. It spreads the force of the fastener over more of the material, which stops the head from crushing soft wood or deforming sheet metal, and stops the hole from enlarging under load. It also gives a nut a smooth face to turn against, so tightening does not chew the surface it bears on.
Compare it with the lock washer, which does the opposite job. A flat washer spreads load; a lock washer resists vibration. The pair is one of the boundaries the Shop Information subtest is built on, and the questions are usually written to exactly that boundary — read what the stem asks, spreads the load or resists loosening, before choosing.
A fender washer is the same idea at a larger diameter, used where the material is thin or soft and the fastener would otherwise pull through. A flat washer does not lock, and it does not keep a joint tight on its own.
Taught in
Related terms
- lock washer — A lock washer is a split or toothed washer that bites into the nut and the work and holds the fastener tight against vibration, so a bolt does not walk loose.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)