2-pack Original Factory Replacement FC40R1078 24″ x 24″ x 5″ (actual size 23 3/4″ X 23 3/4″ X 4 3/8″) MERV 10 Replaces older Honeywell model number F35R. The FC40R Return Grille Filter is a high-efficiency, long-life replacement for return grille applications. It captures a significant amount of the airborne particles in the air that circulate through the filter. (Honeywell recommends allowing a depth of seven inches behind the grille to provide space for the deeper filter and airflow through the filter.) Honeywell recommends changing your filter once a year. It may be necessary to replace it sooner depending on the conditions in your home. Filter features 1″ lip around upstream side FEATURES . Mounts in most third party return filter grilles (features integral gasket around upstream side of filter). . Provides high-efficiency alternative to one-inch filter. . Captures particles as small as 0.3 micron. . Pleated filter for greater media capacity.