... as the seals for welding, card sets, expanding fittings, and machinery, to avoid the leakage of the oil, ... , used to seal threads and flange connection.Ring includes a metallic ring and a rubber gasket. Usually ... as the seals for welding, card sets, expanding fittings, and machinery, to avoid the leakage of the oil, ... of the simple structure, efficient seal, and its reasonable price, it is used widely ...