Conical washer connect with hex nut, it is one kind of self-locking nut. 1.size:M3-M20 2.material: carbon steel, stainless Item: K-NutSize: M3-M20 Material:carbon steel, stainless steelFinish: Natural, zinc-plated, Nickel-plated, black oxide and so on.Package:25kg/carton,or according to customers' requirement