This is a complete 20"x 20" HVAC return air filter grille kit. This kit includes one filter grille,  one 20"x20" 26 gauge  galvanized metal filter box 5" deep with 3/4" flange, one 18" dovetail collar 4" long, one 20"x20"x1" Merv-11 filter and 4 mounting screws. The 18" collar hole will be cut centered in the metal box for you to install the 18" dovetail collar. Connect this kit to your return ductwork with your provided metal pipe or 18" flex. Outside dimensions of the filter grille is 22 5/8 "x 22 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.