Made from specially engineered, glass-filled polymers to ensure greater strength, cooler running & more resistance to wear. Stringently designed and analysed to maintain perfect integrity. Made with smoother surfaces and tighter tolerances to reduce vibration and enhance belt life. Come with lubricated ball bearings & high temperature seals Dayco Idler Tensioner Pulley Dayco No Slack Idler/Tensioner Pulleys Designed to replace serpentine and V-belt drive idler and tensioner pulleys. Daycos reputation for top performance idler and tensioner pulleys is the result of the advanced automotive technologies employed in the materials research, design engineering and manufacture of our pulleys. Specially formulated glass-filled polymers insure a high strength, cooler running, wear resistant "plastic" pulley. The use of state-of-the-art 3-D computer aided design (CAD) and finite element analysis (FEA) guarantees the optimal design and maximum structural integrity for both plastic and steel pulleys. The manufacture of pulleys with smoother surfaces and tighter dimensional tolerances translates into less vibration and therefore longer belt life. Lifetime lubricated ball bearings and double high temperature seals assure peak bearing performance the most critical element of a pulley's service life.