MOST SECURE CAT PORTAL YOU CAN FIND: Most pet doors for cats fasten with flimsy tape. But this kitty door attaches firmly with sturdy screws. Installs in minutes; stays snugly in place KEEPS BIGGER DOGS AT BAY: This large cat door stops your big-breed dog from getting into the cat food & kitty litter NO ANNOYING FLAP: Ever try training a cat to use a flap-covered pet door? It's an exercise in frustration. Fortunately, our cat door is 100% flap-free, so your pudgy feline can walk right through FITS SOLID and HOLLOW DOORS: Unlike most big cat doors, our cat door fits interior doors. Unique design keeps cat's paws from getting stuck inside hollow-core doors Specification: Material: ABS Plastic Frame size: Height 22.5cm; Width 27cm; Thickness 5.5cm Inner frame size: inner diameter 17.5cm; Inner groove thickness 3.5cm Package Included: 1 Set Cat Door (with screws and screws cap) Warm Tip: Because the thickness of each door is different, if there is a problem of inappropriate screws during installation, you need to buy them separately. It can be directly glued on the glass with glass glue