The flat transition duct 45-degree elbows are used for changing the vertical direction of the rectangular duct. They are fitting to use when needing to make tight corners and are utilized for maintaining the best airflow for maximum efficiency in your HVAC system. These galvanized or stainless-steel elbows are mechanically bent, resulting in a non-seamed tubing that can be fitted with a rolled-lipped collar or an angle ring flange.