With the '2002,' an inert gas, such as nitrogen, is injected and sealed inside the hollow metallic O-ring, which makes it appropriate for a high-temperature environment. The pressure of the inert gas inside the O-ring can range from 35 to 105kgf/㎠. A metallic ring becomes weaker in terms of elasticity and hardness at a high temperature. If external pressure is applied when the metallic ring becomes weaker, it can easily be deformed and lose its sealing performance. However, if it is filled with a gas, the gas expands in the hot temperature and works as a spring, allowing the O-ring to maintain its elasticity.