S&S Cycle Primary Chain for Harley Engineered for high-performance Big Twin builds, this heavy-duty primary chain is designed to handle significant torque loads. Each component is heat-treated and precision-machined in the Usa, reducing stretch and wear to ensure accurate valvetrain timing and power transfer. It serves as a robust upgrade for those seeking durability and low maintenance while maximizing machine performance. Features: Direct OEM Replacement 11 Stronger Increased Chain Life Replaces OEM 40037-79