This ring seals the interface between the hydraulic cylinder rod and its cover, preventing fluid leakage and maintaining system pressure. It sits in the groove machined into the cylinder cover, where it compresses against the rod surface during extension and retraction cycles. A worn or extruded ring allows hydraulic oil to bypass the rod seal, which leads to visible external leakage and a gradual loss of cylinder force. As an original component, the ring is manufactured to the same cross-section and material hardness as the factory seal, so it seats fully in the groove without requiring shimming or adapter rings. On reinstall, clean the groove thoroughly and lubricate the ring before assembly.