Couplings slip Within the finishes of two round ducts to generally be joined together after which sheet metal screws are fastened to hold it in position. Couplings may be expected at a specific size like connections 18” and larger. The shaded region in the image beneath may be the coupling. https://oval-conduit90012.blog-kids.com/36999893/top-latest-five-oval-conduit-urban-news