ACDelco 38409 Professional Automatic Belt Tensioner and Flanged Pulley Assembly with 2 Bolts Ensures proper belt tension, alignment, and damping for superior performance Patented vibration damping system increases tensioner, belt, and accessory component life for long lasting use Torsional round spring design provides consistent tension and does not allow contamination for enhanced durability Provides full line coverage for domestic, import, and heavy duty applications