Black oxide bolt is carbon steel fastener with black oxide finish. Black oxide is a chemical conversion coating, not electroplating. It creates a matte black surface on steel. It offers mild corrosion resistance and excellent anti‑friction property. Main function is anti‑rust for short‑term protection and reduction of friction during assembly. It cannot provide heavy corrosion protection for outdoor wet environment. Widely used for machinery, mold, automotive and indoor steel structures. Common grades: 8.8, 10.9, 12.9