The wavy shape flexes like a spring to keep nuts and screws secure on slightly uneven surfaces. These washers add a small amount of tension to stop fasteners from backing out due to mild vibration. While they don't hold as well as other lock washers, they do grip slightly better than curved washers. They work best in electrical panels, light fixtures, and other light duty assemblies. Since these washers hold their shape when untightened, you can reuse them a handful of times without losing strength.