Premium Material: Starlock internal tooth washers are made of high quality 65Mn metal steel, which is a black oxide coating on the metal surface for protection against rust, corrosion and durability. It has high hardness and good toughness that is not easily deformed during use. It can normally be locked onto materials such as plastic and steel. Easy to Use: Starlock internal tooth washers are made of high quality 65Mn metal steel, which is a black oxide coating on the metal surface for protection against rust, corrosion and durability. Rapid rotation exerts a spring force between the fastener head and the substrate, which keeps the washer firmly fixed and creates more friction and resistance to rotation. Easy to store: All the safety rings in the range are packed in a strong transparent plastic case, easy to use, find and carry and can also be used as a storage box. Wide applications: These Starlock washers are widely used for machinery, furniture, tables, DIY enthusiasts, electrical