These washers are manufactured and tested to strict U.S. military standards for material and construction. As you tighten, the uneven ends bite into the nut or screw so it won't loosen due to mild vibration. While they don't hold as tightly as other lock washers, they are a great fit for electrical panels, light fixtures, and other light duty assemblies. Split lock washers are not reusable, and they only work with fasteners that have right-hand threads.