... standard, American standard and DIN standard Kinds of screwed half coupling: bends, elbows ,tees, crosses, sockets, caps, backnuts, flanges, ... 4" 5" 6" Useage of screwed half coupling: conncet cali duct, water pipe, fire-fighting equipment or other gas, water ,oil ... steel ,stainless steel ,alloy steel . Surface of screwed half coupling: cold galvanizing,hot galvanizing,and black Egdes: banded, beaded ...