Speedi-Products SM-RDP 63 6-Inch by 3-Inch Round Galvanized Plain Reducer 6-Inch x 3-Inch Galvanized Sheet Metal three piece reducers Used to reduce the diameter of a HVAC supply, return or exhaust round duct Seal joints with approved duct mastic sealants Insulate Ductwork for improved energy efficiency and comfort Consult your local building codes for approved installation practices