This adjusting washer sets the axial clearance between rotating and stationary components in a disc mower's cutter bar assembly. It sits between the bearing housing and the gear or disc hub, taking up stack-up tolerances so the preload on the tapered roller bearings remains within specification. A worn or missing washer allows excessive end float, which leads to gear tooth misalignment, increased vibration, and accelerated bearing wear. Because the washer thickness directly controls the running clearance, replacing it with the original specification restores the correct preload without requiring shim stacks or additional machining. On reassembly, clean the mating faces and verify the bearing spin torque after installation.