Sandwich Style Insulated Round Duct, Rectangular, Door Width 16 1/2 in, Door Height 12 3/8 in, Duct Diameter 21 in to 22 in, Material Steel, Finish Galvanized, Rough Opening Width 15 3/4 in, Rough Opening Height 11 7/16 in, Temp. Range 200 Degrees F max, Hinges None, Standards SMACNA, Includes Duct Diameter 25 in to 28 in, Insulated Access Door 16 in x 12 in