Our pre-fabricated Damper slides save you time and money during your Smoker Project. Easy installation, simply cut the required size hole in your firebox and install this kit by stitch welding it over the hole. 40 square inch. This 4 x 11 intake damper has a 4 x 10 hole for 40 sq in of air. More compact design with position markers. Replaces our 3 x 12 slide damper which was 36 sq inch intake air.