Couplings slip Within the finishes of two round ducts to get joined together after which sheet metal screws are mounted to carry it in position. Couplings might be required at a particular measurement for instance connections eighteen” and larger. The shaded region while in the image underneath is the coupling. https://miloshwly.rimmablog.com/35682022/5-tips-about-round-conduit-you-can-use-today