This friction disc is the outer rear plate in the PTO clutch pack. It transmits torque from the engine to the PTO shaft when the clutch is engaged. The disc sits between the inner friction plates and the pressure plate; its outer diameter registers against the clutch housing to react the torque load. Wear on the friction faces reduces clamp force, leading to PTO slip under load and eventual engagement chatter. The disc is manufactured to the original material and surface-finish specification so that the clutch pack's engagement timing and torque capacity match the driveline design. On reassembly, inspect the mating surfaces for scoring and replace the retaining snap ring if deformed.