A ring of spring steel cut through and twisted into a slight helix, so its sharp ends dig into the nut and the joint surface as it flattens. Transverse vibration testing shows that once the washer is flat it offers almost no resistance to self-loosening, and on hardened surfaces it can even help a nut back off. Its real use is as a weak spring on soft, low-preload joints.
Customer wants split lock washers on everything, so they go on, but the real lock on this joint is the preload.
If an engineer asks what locks the joint, the right answer is preload; the split washer mostly comes along for the ride.
Also heard as
- lock washer
- spring washer
- helical spring lock washer
Related terms
Self-loosening
A tightened nut or bolt turning loose by itself, usually because sideways slip in the joint lets it walk off.
Belleville washer
A dished, conical spring washer that flattens under load and keeps clamp force on a joint as it settles or expands.
Prevailing-torque nut
A nut built to resist turning on the thread before it seats, using a nylon insert or deliberately distorted threads.
Preload
The tension created in a bolt by tightening it, which clamps the joint and keeps it from slipping or opening.