This tapered ring sits on the pulley shaft in the threshing drive of a self-propelled forage harvester. It transmits torque from the pulley to the driven component by creating a clamping force when the retaining nut is tightened. A worn or deformed ring allows the pulley to slip on the shaft, reducing drive efficiency and causing uneven belt wear. The manufacturer machines the taper to match the original pulley bore angle, so the ring seats fully without requiring shimming. On reinstallation, clean the shaft and bore surfaces and torque the retaining nut to specification.