Decorative Vent Cover for a 18x6 Opening. Resin Paint Grade Grille Can Be Used As Return, Supply, Foundation Vent, Register. Cosmo Design 20x8 Overall Size Important: Main picture shown is a 12x6 grille (overall size approx. 14x8) Choose size based on your opening. There is a 1/4" lip on the back of the grille, it is not completely flat. (see pic 2) Grille will come with predrilled countersunk screw holes and screws Grille is unfinished polyurethane material and will need to be painted by you. Grilles are for wall or ceiling use only. Not for floor use.