Product Details: The Dayco Serpentine Automatic Belt Tensioner for Mack is designed to provide reliable belt tension, alignment, and dampening of harmonic vibrations. This tensioner features a steel pivot tube on specific designs for enhanced stability, zinc coated mounting bolts that resist rust, and thermoplastic rubber spring slot plugs and rubber O-ring seals to help keep contaminants out. This tensioner is designed to provide reliable performance and long-lasting durability for your vehicle. FleetPride is your First Click in Heavy Duty®.