HIGH-QUALITY CARBON STEEL: Made of high-quality carbon steel, these nuts have high hardness and long service life. GOOD RUST RESISTANCE: The surface is coated of zinc for good rust resistance and better performance. 20PCS NUT: There are totally 20pcs nut, which you can use for many projects. PROPERTY: They are easy to use and convenient for joining aluminum profiles to other parts. APPLICATION: This hammer nut is mainly used for type 40 extruded aluminum profiles.