The round seal ring, code 100100, is a sealing element used in the MAN L21/31 engine to prevent unwanted passage of fluids or gases between adjoining components and to maintain the required tightness of the relevant engine system. Its circular form allows the ring to provide continuous sealing around the connection, with compression between mating surfaces creating the barrier necessary to retain the operating medium. Depending on its installation position, it may be exposed to lubricating oil, fuel, cooling water, compressed air, temperature fluctuations, pressure changes, vibration, and mechanical movement. For this reason, the correct dimensions, material compatibility, surface condition, and installation procedure are essential for preventing premature wear, deformation, hardening, or loss of sealing performance. A correctly installed round seal ring helps minimize leakage and contamination, protects associated engine components, supports efficient maintenance, and contributes to the long-term reliability and operational safety of the MAN L21/31 engine.