Broan 639 Wall Cap for 3-1/4" x 10" Duct for Range Hoods and Bath Ventilation Fans Overall sizing is 12-3/4" wide x 5-5/8" high. Duct fitting protrudes 4-7/8" from back of cap to allow proper fit to the ductwork (NOT for use with dryer venting) Equipped with a spring-loaded backdraft damper and bird screen to keep nests and small animals on the outside Wall cap is made of 24 gauge CRCQ steel construction with a black electrically-bonded epoxy finish for durability and long life Sold as 1 to a carton