This sealing ring fits into the piston rod gland of a hydraulic cylinder. It sits in the groove machined into the gland bore, where it contacts the rod surface to prevent pressurized fluid from leaking past the rod during extension and retraction. A worn or hardened ring allows external oil leakage, which reduces system pressure and can contaminate the machine exterior. Corteco manufactures this ring to match the original seal-groove geometry, so the cross-section fills the groove without over-compression or under-sealing. On reinstallation, inspect the rod surface for scoring and lubricate the ring before assembly.