36"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 37.75"w x 21.75"h] Fixed Blades and other areas where baseboard-mounted 14" Round Duct Pipe FR M 414 White For 10 duct opening

and other areas where baseboard-mounted return air grilles are required

24"w X 6"h Is The Size For The Duct Opening Measurement Only

actual front end outer dimensions are 21

Actual Front End Outer Dimensions Are 12" Width X 5" Height - SEE IN DESCRIPTION HOW TO MEASURE A GRILLE

+ Product Details Perfect Fit & Easy Sizing - Designed for a 10" x 16" or 16" x 10" duct opening (measured at the opening)

36"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace Weather Resistant Air Grille with Screen Mesh [Outer Dimensions 37.75"w x 21.75"h] Fixed Blades and other areas where baseboard mounted 14" Round Duct Pipe FR M 414 White For 10 duct opening and other areas where baseboard mounted return air grilles are required 24"w X 6"h Is The Size For The Duct Opening Measurement Only