A 30mm PU Piston O-Ring is a sealing component made from Polyurethane (PU), specifically designed for use in hydraulic or pneumatic systems. The 30mm refers to the outer diameter of the O-ring, which is typically measured in millimeters. These O-rings are primarily used to provide a reliable seal between the piston and cylinder, ensuring the effective operation of hydraulic or pneumatic systems by preventing fluid leakage and maintaining pressure.