Glossary
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.
A lock washer is a washer with a spring in it. The common split-ring type is a disc with one radial cut, its ends offset like a wave, so that tightening the fastener flattens the ring and leaves a load pushing back against the nut. The toothed type has teeth that bite into nut and work instead of relying on spring.
Its job is not area, it is time. A joint under vibration — an engine mount, a mower deck, a bracket bolted to something that shakes — tends to walk a plain nut loose. A lock washer raises the friction the nut must overcome to turn backwards, which is why this subtest's boundary line reads resists loosening under vibration.
A lock washer is not a seal, and it is not a substitute for a flat washer. A lock washer cannot spread load, and its teeth die into a soft surface, so the two are often stacked: one spreads the load, the other holds it.
Taught in
Related terms
- 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.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)