4-1/2 x 18-1/2 to 10" Round Transition for Range Hoods and Bath Ventilation Fans(P)Maximize the air and sound performance of your Broan ventilation fan or range hood using one of our wide variety of ducting accessories.( P)(UL)(LI)Overall size of this horizontal left transition is 20 1 2" from front to back, 12" high and 10" wide with a "right end boot" to give you the right fit for your installation( LI)(LI)Transition is made of 26 gauge galvanized steel construction for durability and long life( LI)(LI)Sold as 1 to a carton(