The metal winding pad is divided into four specifications, which are A, B, C, and D. Type A is the basic type, that is, without a ring, completely wrapped by metal and non-metal belts, suitable for tongue and groove surfaces. Type B is the inner ring type, suitable for MFM surface; Type C is the outer ring type, suitable for RF surface, but the pressure is lower than 6.3MPa; Type D is the inner and outer ring type, for example: the gasket is type 0220, which is type A pad, without a ring, the metal belt is 304, and the non-metal is graphite. 0221 is the B-type pad, with an inner ring, the metal belt is 304, and the non-metallic belt is flexible graphite. We often say that the metal graphite winding pad or the metal asbestos winding pad, generally X22X type and X21X type, X is determined according to the flange surface.