Whenever a bolt or eye-bolt is used to attach a harness to your vehicle, you should use these wavy washers. One on each side of the sheet metal. They will help keep the bolt from backing out. These are not needed when using the machined sleeve/washer setup for pivoting bolt-in brackets. TAKATA also recommends using some form of thread locker.
WASHER SIZE:
HARNESS ACC - BOLT-ON WASHER (3/8" M10) - TR-S83
