Couplings slip inside the finishes of two round ducts to become joined jointly and afterwards sheet metal screws are fixed to carry it in place. Couplings may be needed at a specific sizing like connections 18” and bigger. The shaded space inside the impression underneath is the coupling. Usually the https://oval-conduit69901.aboutyoublog.com/42788551/5-tips-about-oval-conduit-you-can-use-today