Engine vibrations can loosen standard fasteners quickly. Lock washers prevent this by keeping the joint under tension. A split lock washer acts like a spring, pushing back against the bolt head as you tighten it. Tooth lock washers have sharp teeth that bite into the mating surfaces. They are cheap, simple, and effective for non-critical bolts like brackets and electrical grounds. Never use them on high-torque joints like cylinder heads or main bearings.
Mechanic Glossary
Lock Washer
A split or tooth-edged spring washer designed to create constant tension and friction, preventing nuts and bolts from backing out due to vibration.
Frequently Asked Questions
The flat side or body sits against the bolt, while the split ends or teeth face the material surface.
Do not reuse them. Once flattened, they lose their spring tension and will not lock effectively a second time.
Threadlocker is usually more reliable on critical components, but lock washers are faster and easier to install on basic chassis parts.
Yes. The sharp teeth or split edges will gouge aluminum or plastic. Use a flat washer underneath or switch to threadlocking compound instead.