24" X 8" Baseboard Return Air Grille - HVAC Vent Duct Cover - 7/8" Margin Turnback For Flush Fit With Baseboard Work - White Insulated Line + Product Details Size -

+ Product Details Size - 8"w X 12"h is the size for the duct opening measurement only

Actual Filter Size – 25 3/4"w x 5 3/4" x 1"

and then smoothly drop in the grill

Ideal for Walls & Ceilings: Designed for seamless installation in standard 12" X 12" duct openings

+ Product Details Size - 40"w X 6"h is the size for the duct opening measurement only

24" X 8" Baseboard Return Air Grille - HVAC Vent Duct Cover - 7/8" Margin Turnback For Flush Fit With Baseboard Work - White Insulated Line + Product Details Size -+ Product Details Size 24"w X 8"h Is The Size For The Duct Opening Measurement Only, Actual Front End Outer Dimensions Are 25. 75" Width X 9. 75" Height SEE BELOW IN DESCRIPTION How To Measure A Grille Powder Coat Finish Smooth, shiny, scratch resistant, beautiful. Looks like it was just waxed. High Quality Easy unrestricted airflow for your HVAC system 7 8" margin turnback. Carefully Shrink Wrapped With cardboard backing to prevent damage in shipment