This O-ring seals the connection between the three-point hitch linkage and the hydraulic cylinder rod. It prevents fluid leakage at the rod gland, maintaining system pressure for lift and lower operations. A worn or compressed O-ring causes external oil seepage and a gradual loss of lift capacity. The ring is sized to match the original groove depth so the seal compresses correctly against the rod surface. On replacement, clean the groove and lubricate the ring before installation.