Speedi-Products SM-OTRS 05 6.125-Inch x 3-Inch Oval to a 5-Inch Round Straight Boot 5-Inch Oval to Round Straight Boot For transitioning Oval Wall Stack ducting to Round Sheet Metal Pipe For interior wall supply and return air ducts Seal joints with approved duct mastic sealants Insulate Ductwork for improved energy efficiency and comfort