Hart & Cooley® Return Air Grille, Series: RH45, 18 x 18 in Size, 17-1/2 in Duct Width, 17-1/2 in Duct Height, 19-3/4 in Overall Width, 1 in Overall Depth, Fixed Blade Grate, 580 to 1500 cfm Flow Rate, 1.46 sq-ft Effective Area, 45 deg Deflection Angle, 3/4 in Blade Spacing, Aluminum, White Painted, Domestic