18" Concentric Curb Transition

18" Concentric Curb Transition, Duct Size:18", Designed to Drop Into The Curb and Convert The Square Duct Unit Connections to Round Duct, For Use with S1-1RC0501, S1-1RC0502, S1-1RC0503, S1-1R0504 Roof Curbs, Dims:10"H X 17-1/2"W X 21"D, Weight:9 Lbs, In Box, Made in USA.