18"W X 18"H [Duct Opening] 4-Way Aluminum Curved Blade Adjustable Air Supply HVAC Diffuser [Outer Dimensions: 19.75"W X 19.75"H] steel Actual Filter Size – 31

Actual Filter Size – 31 3/4"w x 27 3/4" x 1"

+ Product Details Size – 8"w X 30"h is the size for the duct opening measurement only

High Quality – High quality ABS plastic will never rust

Actual Filter Size – 35 3/4"w x 33 3/4" x 1"

18"W X 18"H [Duct Opening] 4-Way Aluminum Curved Blade Adjustable Air Supply HVAC Diffuser [Outer Dimensions: 19.75"W X 19.75"H] steel Actual Filter Size – 31+ Product Details Size 18"w X 18"h is the size for the duct opening measurement only, actual front end outer dimensions are 19. 75" width X 19. 75" height. Design Individually adjusting curved blades for better air flow control. Screws Included High Quality Aluminum The premium durable aluminum will never rust and it will never wear through leaving the material with an elegant, beautiful, and smooth surface, adds a luxurious touch to any home.