18 x 24 Rectangular Gable Vent The rectangular gable vent is used to vent the attic. The 2-piece system is fully compatible with all siding profiles, colors, and types. Simply install the base when installing the siding, then snap on the cover later. Rectangular base makes siding cuts easier. Adjustable 5/8 to 1-1/4 for use with all siding styles. Each gable vent includes screen protection to keep pests out. Manufactured with ultraviolet-stabilized color, minimizing the effects of exposure to the elements. Rich textured appearance. Outside dimensions 18 x 24 . Ventilated opening dimensions 16 x 20 . Surface Dimensions 18 x 24 , Shape Rectangular, Color White, Opening Dimensions 16 x 20 , Material Vinyl, Net Free Area 99.4 sq in, Pkg Qty 1, Package Type Box