304 high quality stainless steel. Stainless steel is a common material with a density of 8 g/cm3, also called 18/8. It has good handling and high tenacity up to a temperature of about 800 degrees. Different sizes of plate washer: M3 30PCS,M4 30PCS,M5 40PCS,M6 35PCS M8 40PCS,M10 40PCS,M12 10PCS,to meet different needs.It is a very essential manual tool for the family. With the plate washers, the spring washer device is used under the nut to prevent the nut from loosening. Grower washers are used for loosening, flat washers have no loosening function and flat washers only increase the contact surface. The plate washers are arranged in a storage box, which allows you to find yourself in the series easily and avoid loss if needed. Application: perfect for electrical connections on household and commercial appliances, automotive and marine uses in which the energy source has a threaded / bolt-type connection.