This disc spacer positions the PTO shaft assembly axially, maintaining the correct clearance between the clutch pack and the housing. It sits on the output shaft between the retaining nut and the bearing inner race. A spacer that is too thin or too thick alters the preload on the bearing, which can cause shaft end-play or excessive bearing heat. This original part is machined to the same face-parallelism and thickness tolerance as the factory spacer, so the clutch engagement depth and bearing preload remain within the design specification. On reassembly, verify that the spacer sits flat against both mating faces before torquing the retaining nut.