Prime-Line 9082839 Lock Washers, Internal Tooth, 1/2 in., Zinc Plated Steel, 25-Pack

Internal tooth lock washers feature teeth that help to prevent loosening of a nut or bolt by digging into the surface. For maximum holding power, use one between the surface and the bolt head, and use another one between the surface and the nut. It is best to use these with smaller bolt heads and in applications where there is a desire to not have exposed teeth. Lock washers are great for use in cases where the bolt may be subject to vibration.