Specifications: Material: Steel 65Mn Finish: Black Inner Diameter: M20 Outer Diameter: 40mm Thickness: 2.5mm Color: Black Package Content: 50 x Starlock Washers Description: 1. Material: high quality steel 65Mn, hard and durable; 2. Product Type: Starlock Printer BLOCK. 3. Application Widely used in equipment machinery, industrial production of shock and insulation. 4. Easy to install: sturdy and durable, high corrosion resistance for equipment and substrate, easy to install. 5. Product Features A lock washer exerts a spring force between the head of the fixings and the substrate to create more friction and rotational resistance.