Flat Oval Spiral Duct View the underneath video to see the set up of oval duct and fittings. Discover the reducer being used is undersized on its collar permitting the oval duct to slide over the collar. They may be using Unistrut with threaded rods as hangers to the ductwork. https://caidenzrgti.blogoscience.com/43108198/round-conduit-can-be-fun-for-anyone