Couplings slip In the finishes of two round ducts to generally be joined jointly and then sheet metallic screws are fastened to hold it in position. Couplings could be necessary at a particular sizing like connections 18” and bigger. The shaded location inside the impression below is definitely the coupling. https://ovalconduit34456.bloggerswise.com/44434695/getting-my-round-conduit-to-work