This variable speed belt transmits power from the engine to the fan drive, allowing the fan speed to be adjusted in relation to engine RPM. It sits between the crankshaft pulley and the fan hub, where its toothed profile prevents slippage under varying load conditions. A worn or glazed belt loses grip and causes the fan to under-speed, reducing cooling airflow through the radiator and hydraulic oil cooler. The belt is manufactured to the original tooth profile and pitch length, which maintains proper engagement with both pulleys and keeps the tensioner within its working range. When replacing, inspect the pulleys for wear and set the tensioner to the specified deflection.