Speedi-Products SM-W3106 NB 10-Inch Width by 3.25-Inch to 6-Inch Width Stack 90-Degree Boot 6-Inch Wall Stack 90 Degree Boot For transitioning Rectangular 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