Item Descriptions:-Fit for bolts, screws and other fasteners of the corresponding size to prevent loosening and make the screws fit the machine better.-Made of manganese steel, it is more wear-resistant and resistant to strong impact. The surface is galvanized and is not easy to rust.-The surface of the washer has a precise geometric shape to better prevent the fastener from sliding. Tension is used instead of friction to tighten to obtain a better and safer grip.-Fit for electrical connections of domestic and commercial appliances, automotive and marine applications.etc.-The package includes 30 pairs, and there are 5 sizes to trouble your different needs, each size of 6 pair. Size: 8.7x13.5x2.5mm/0.34x0.53x0.098in; 10.7x16.6x2.5mm/0.42x0.65x0.098in; 13x19.5mmx2.5/0.51x0.77x0.098in; 17x25.4x3.4mm/0.67x1.0x0.13in; 21.4x30.7x3.4mm/0.84x1.25x0.13inPackage:6 Pair M8 Lock Washer6 Pair M10 Lock Washer6 Pair M12 Lock Washer6 Pair M16 Lock Washer6 Pair M20 Lock WasherItem Specifications:Material:Manganese steelSize:M8/M10/M12/M16/M20Quantity:30 Pairs