This martin house adapter was origianlly designed by Del McKinnon with a round hole and a crescent. I expanded upon it and made it a round hole and an Excluder entrance. This plate offers the versatility of a round hole and an Excluder entrance. You can start with a round hole, and then, once you have birds, turn the plate over and have an Excluder entrance. The plate measures 5 3/8" tall and 4 7/16" wide. The bottom of each hole is 1/2" from the bottom of the plate. The TW-24A sells for $3.75 each plus S&H.