Dayco No Slack Idler/Tensioner Pulleys Designed to replace serpentine and V-belt drive idler and tensioner pulleys.Dayco’s 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.