Flat Oval Spiral Duct Look at the underneath online video to see the installation of oval duct and fittings. See that the reducer being used is undersized on its collar allowing for the oval duct to slip above the collar. They are really utilizing Unistrut with threaded rods as hangers https://elliotwodsg.digitollblog.com/36523280/the-best-side-of-round-conduit