The O-ring is used to prevent the leakage of vapors from Breathing Circuit Gas (BCG) in an anesthesia delivery machine. A common cause of vapor leakage is the absent or damaged O-ring. It is used in the flow meter assembly of a simple anesthesia machine, there are tubes through which gases flow to the outlet. O-rings are fitted at the ends of flow meter block for sealing purpose to avoid leakage. It is the most common type of seal used in a wide range of static or dynamic applications.