50PCSM6 spring lock washer, fastener size: 1/4 ", material: stainless steel, black surface, highest form of corrosion-resistant steel. It has excellent corrosion resistance in harsh environments such as high temperature, cold weather, and high humidity; excellent rust resistance, excellent oxidation resistance, and long service life. The spring washer is compatible with nuts and bolts of the same size, used to evenly distribute the load of screw tightening to prevent loosening of bolts and connecting objects. The split lock washer provides a circular support surface with a biased split end, which helps to bite into the mating material to provide locking function when tightened under the nut. Widely used - suitable for fields such as electronics, machinery, automobiles, ships, industry, furniture, etc.