This is a complete 12"X12" HVAC return air filter grille kit. This kit includes one 12"X12" filter grille, one 12"X12" 26 gauge galvanized  metal box 5" deep with 3/4" flange, one 10" dovetail collar 4" long, one 12"x12"x1" Merv-11 filter and 4 mounting screws. The 10" collar hole will be cut centered in the metal box for you to install the 10" dovetail collar. Connect this kit to your return ductwork with your  metal pipe or 10" flex. Outside dimensions of the filter grille is 14 5/8" X 14 5/8". Please check out our store and our other ductwork. We specialize in fabricating the highest quality ductwork available with the quickest turnaround time in the industry. Our goal is to make the installation of your HVAC equipment as easy as possible. We do this by providing you with the best price, products, and customer service you expect and deserve. We are always here to help until your project is completed and you're completely satisfied.