Dayco 89451 Belt Tensioner Features a patented flat spring design that's engineered to handle the higher torque and power pulses exerted by today's diesel engines Rugged pulleys with double lifetime lubricated bearings deliver long lasting, dependable service Features an extremely damped design using a wave spring and a metal ring with a bonded rubber surface to act as a radial shock absorber for the tensioner arm Heavy-duty cast aluminum body and pulley arms translate into extra strength and durability