Washer, spring, medium square, olive dipped, GR 4.8, M18, Fastbolt.

Square spring washers, also referred to as split lock washers, are designed to provide a ductile spacer with vibration resistant properties. It is similar to a split spring washer, in the way that it has a split in the washer to increase flexibility, but instead features a square profile. Olive-Drab produces a heavy olive drab chromate coating on zinc or cadmium plated surfaces. It provides the maximum salt spray and abrasion resistance of any type of chromate dip.