The "SI" type is a spiral-wound gasket, which is made by sending metal rings of various materials with a thickness of 3.0mm or 3.2mm to the inner side of the basic gasket. Internal wheels prevent deformation of the gasket body to the inner side during overcompression and reduce the gap between the inner diameter and the inner diameter of the gasket to prevent fluid from staying or corrosion of each flange. It is mainly used for connections such as Male & Female Flange, Female Flange, Valve Bonnet, or various pressure vessels.