Stop nuts and screws from loosening due to mild vibration. As you tighten, the uneven ends bite into the nut or screw so it won't back out. While they're not as vibration resistant 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.

Blue-Dyed Steel—These metric-sized washers have a distinctive blue color, so you can easily tell them apart from inch washers. The coating provides only minimal corrosion resistance, so these washers are best for dry environments.