12" X 4" [Duct Opening] 1-Way Air Vent Adjustable Aluminum Curved Blades Integral Multi-Shutter Damper HVAC Diffuser [Outer Dimensions: 13.75"W X 5.75"H] 18in diameter actual front end outer dimensions

actual front end outer dimensions are approximately 8

It has an outer surface made of high-quality aluminum foil and an inner surface made of metalized PET with inside high-tensile spring steel wire

The first number in a grille size

4" X 14" Brass Victorian Floor Register Grille - Modern Contempo Decorative Grate - HVAC Vent Duct Cover - Brass Plated

Actual Filter Size – 31 3/4"w x 35 3/4" x 1"

12" X 4" [Duct Opening] 1-Way Air Vent Adjustable Aluminum Curved Blades Integral Multi-Shutter Damper HVAC Diffuser [Outer Dimensions: 13.75"W X 5.75"H] 18in diameter actual front end outer dimensions+ Product Details Size 12"w X 4"h is the size for the duct opening measurement only, actual front end outer dimensions are 13. 75" width X 5. 75" height. Design Individually adjusting curved blades. Multi shutter damper with handle operator to adjust air flow. 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