This ring seals the connection between a hydraulic hose and its fitting, preventing fluid leakage at the coupling point. It sits in the groove of the hose end or fitting face and compresses when the connection is tightened, creating a positive seal. A degraded or missing ring causes external oil loss and air ingress, which leads to erratic actuator response and pump cavitation. The original part matches the groove geometry of the host tractor's hydraulic fittings, ensuring the correct compression force for a leak-free joint. Replace the ring whenever the hose is disconnected; clean the sealing faces before installation.