This pet screen door is made of quality ABS material, durable and sturdy. Build-up the provided screws with nuts onto this dog door frame would enough sturdy and never fall down easily, the door flap can be replaced anytime. Built magnetic into the door frame can keep automatically closing when your dog sliding the screen door, even you can lock the door by the 2 sides blue lock if you would like to prevent your pets from walking freely. Only install this pet door into interior/exterior screen door, window and any other screen areas, can not be used for very thick wooden doors, iron/aluminum doors, walls. Installation manual attached, easy to install. Small: Inside flap opening size: 8 x 10 inch, outside frame size: 9.4 x 11.4 inch, suit for small dogs, cats or other small pets go in and out freely. Large: Inside flap opening size 12 x 14 inch, outside frame size 14 x 16 inch, suitable for small to large dogs, cats or other pets go in and out freely, not recommend for super large dogs.