Package Includes: 7 sizes of M3 / M4 / M5 / M6 / M8 / M10 / M12 in total 340 pieces, in a transparent box, applicable to different sizes of fasteners. High Quality Materials: Made of 65Mn metal steel, black oxide finish, no burr, providing good resistance to corrosion and high temperatures. 7 Size: 340pcs starlock washer set includes 7 most used sizes, M3/M4/M5/M6/M8/M10/M12, all washers will be packed in a strong transparent plastic case, can be used for storage box. Working Principle: A lock washer exerts a spring force between the fastener head and the substrate, which holds the washer hard against the substrate and the bolt threads hard against the nut or substrate threads, creating more friction and resistance to rotation. Wide Range of Applications: Used in machinery equipment, industrial production of shock absorption and insulation, can meet your different needs in daily life. High quality internal tooth Starlock washer assortment sets, perfect for quick fixes and very simple