The Sureflap Microchip Cat Flap is suitable for cats and has a flap opening of 142mm (W) x 120mm (H) - This dimension is the smallest area of the cat flap that your cat will have to enter through. he cat flap works by reading your cat's existing identification microchip (no collar required), compatible with all international microchip formats, stores up to 32 microchip numbers, runs on 4 x AA batteries for over 12 months, two part construction for easier installation, fits into doors up to 6cm thick with no accessories.The microchip cat flap can also be installed in glass from 3mm to 6cm in thickness. A mounting adaptor is required for glass and wall installations (sold separately). For non-micro chipped pets you can use the SureFlap collar tag. Key Features: Selective entry any animal can exit. The microchip reader is located on the outside of the cat flap onlyStores up to 32 pet identities in memory. Remembers all registered cats even when the batteries are removedLow battery indicator light flashes red when the batteries start running low giving you plenty of time to change themUp to 12 months battery life (4 x AA batteries not included). A low battery indicator will flash when the batteries need changing. Manual lock stops your cat leaving or entering the house. Set to in-only to enable your cat to come indoors without being able to get out againWorks with all common identification microchips & RFID collar tags (not included) 3-year warrantyFlap Opening Dimensions: 142mm (W) x 120mm (H) - This dimension is the smallest area of the cat flap that your cat will have to enter. Door/Wall Mounting Dimensions: 165mm (W) x 171mm (H) - The size of hole required to fit your cat flap. Exterior Frame Dimensions: 210mm (W) x 210mm (H) - Size of the exterior cat flap frame. Tunnel Depth: 70mm - Depth of the inside tunnel of the cat flap. Glass Mounting Dimensions: - A circular hole is required to install the cat flap in glass. The optimum hole size is 212mm, but the cat flap can be installed into holes up to 260mm in diameter.