Square washer is a flat washer with square outer shape and round inner hole. It can increase contact surface and distribute clamping pressure. Its square edge prevents spinning when tightening bolts. Materials: carbon steel, stainless steel 304/316. Finishes: blue‑white zinc plated, color zinc plated, hot‑dip galvanized. Widely applied in wood structure, steel structure, photovoltaic bracket and profile installation.