Couplings slip In the ends of two round ducts for being joined jointly and then sheet metal screws are fastened to hold it in place. Couplings could be necessary at a particular measurement for instance connections eighteen” and bigger. The shaded space in the image beneath may be the coupling. https://roundconduit89011.idblogz.com/37131434/not-known-factual-statements-about-oval-conduit