Washer, spring, medium square, chrome, GR 4.8, M16, 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. Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardness.