Amazon.com : SureFlap Microchip Pet Door Connect Without Hub - Flap Opening is 6 3/4 inches by 7 inches : Pet Supplies
Felaqua
Amazon.com : SureFlap Microchip Cat Door Connect with Hub Bundle - Door Opening: The Microchip Cat Door Flap Opening is 5 5/8" (w) by 4 3/4" (h : Pet Supplies