The 'OS' type is a spiral wound gasket with an outer ring. It is manufactured by attaching a metal ring made of various materials with a thickness of 3.0mm or 3.2mm to the outer wall of the basic gasket. When the gasket is compressed, the outer ring prevents transversal deformation from occurring to the gasket. The outer wall of the outer ring is designed to come in contact with the inside of the bolt used to tighten the flange when the gasket is assembled, making the assembly easier. It is mainly applied to raised face flanges, top tank, junctions in pressure vessels, high-temperature-high-pressure equipment, ultra-cold pipe, etc.