This pulley transmits drive torque from the engine or gearbox to the threshing mechanism input shaft. It is mounted on the drive belt path that powers the threshing drum or rotor assembly. A worn or misaligned pulley causes belt slip, reducing threshing speed and increasing the risk of plugging. The manufacturer machines the pulley to match the original belt groove profile and bore tolerance, so the belt tracks correctly and the shaft fit does not require additional shimming. When replacing, inspect the belt for wear and confirm the pulley runs true on the shaft before tensioning the belt to specification.