HVAC Premium Round to Oval Elbow Boot | Galvanized Sheet Metal Oval to Round 90-Degree Boot | 5" Oval to Round Elbow Fitting is Compatible with Duct 5" - Amazon.com
Master Flow 3-1/4 in. x 10 in. Short Way 90 Degree Rectangular Elbow 90E3.25X10 - The Home Depot
Master Flow 14 in. 90-Degree Round Adjustable Elbow 90E14 - The Home Depot