This nest front will fit in your 12x24 nest box. The Foy's Nest Front has a perch board which is where a bird will perch when the entrance door is closed or if the mate is sitting on eggs or young. High quality front with a wide entrance door which measures 6 3/4" wide x 7" high. If you lock your birds into the nest box, the shelf offers you a place to sit feed and water cups. 12" high, 24" long. The landing perch extends out 4 1/4". Custom sizes available.