This O-ring seals the hydraulic lift cylinder at its piston rod or housing interface, preventing fluid bypass during raise and lower cycles. It sits in the groove machined into the lift assembly, where it compresses between the stationary housing and the moving rod. A worn or hardened O-ring allows internal leakage, which causes the implement to drift downward under load or reduces maximum lift height. The original part matches the groove depth and cross-section of the factory seal, so no shimming or adapter is needed during replacement. On reinstall, clean the groove thoroughly and lubricate the ring before assembly.