Machine Adapter For Nominal Duct Diameter 18 in Inlet Diameter 18 in Material Steel Product Type Machine Adapter Material Thickness 20 ga Overall Length 5 1/2 in Maximum Pressure Rating 42 in wc Weight 3.45 lb For Duct Height 18 in Flange Inner Diameter Not Applicable For Duct Width 18 in Flange Outer Diameter Not Applicable Maximum Airflow 12 370 cfm Inside Diameter 17 7/8 in Number of Holes on Flange Not Applicable Overall Width 18 in Bolt Circle Diameter Not Applicable