It is mainly used for the connection between steel plate round pipe and spiral pipe. First, roll both ends of each pipe section out of the drum and narrow one end into a small opening. During installation, the small opening is inserted into the large opening according to the direction of air flow. The outer surface of the earrings is tightly connected through steel hoops, and then fastened with bolts in the middle of the earrings. Plug in connection: mainly used for rectangular or circular pipe connection. First make the connecting pipe, then insert the air duct on both sides, and then fasten it with rivets.