18" x 24" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Color_Red Oak Wood + Product Details Size - 4 X 12 Is CRFG2028 Width_14in

+ Product Details Size - 30"w X 16"h is the size for the duct opening measurement only

The total outer size of this grille is the listed size plus 1

actual front end outer dimensions are approximately 20 5/8" width X 16 5/8" height

+ Product Details Size – 36"w X 12"h is the size for the duct opening measurement only

Looks Like It Was Just Waxed

18" x 24" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Color_Red Oak Wood + Product Details Size 4 X 12 Is CRFG2028 Width_14in + Product Details Size 30"w X 16"h is the size for the duct opening measurement only The total outer size of this grille is the listed size plus 1