This M20 nut secures the threshing drum assembly on the host machine. It is a threaded fastener that clamps the drum components to the shaft, maintaining the alignment and rotational balance of the threshing mechanism. A loose or missing nut allows the drum to shift on its shaft, producing vibration and uneven threshing clearance. The nut is manufactured by Claas to match the thread pitch and seating face of the original drum assembly, so no additional shimming or thread-locking compound is required for proper torque retention. On reinstallation, clean the threads and tighten the nut to the specified torque value.