This washer sits on the threshing unit shaft, between the rotating components and the housing face. It acts as a load-spreading interface that prevents the fastener from digging into the softer material of the adjacent part. A worn or deformed washer allows the clamping load to relax, which can lead to shaft-play and misalignment of the threshing drum. The nose on this washer indexes into a corresponding recess on the assembly, keeping the washer from rotating during operation. On reinstall, verify the nose aligns with the recess and that the washer sits flat before torquing the fastener.