Flat Oval Spiral Duct Look at the down below video clip to see the set up of oval duct and fittings. Notice that the reducer getting used is undersized on its collar allowing for the oval duct to slip about the collar. They are using Unistrut with threaded rods as https://ovalconduit12233.blogsidea.com/43200188/little-known-facts-about-oval-conduit