... steel stair tread 2 Hot dipped zinc coating 3 Painted or untreated 4 Surface Shape: Flat,gear 5 ... leakage area reaches 83.3%, whichis more than two times large than that of cast iron.3,Hot-dip galvanizing: Good ... safety ,and convenient opening.5,Saving investment: With large span, the cost is lower than that of cast ... ,it can be used in the environment with large span and heavy load, such as the wharf ...