The Ideal Pet Window Insert can be used for any sized cat and small breed dogs upto 7″ wide.. This unit is rated the best utility window on the market. It features a generous pet opening for small to larger sized cats all the way to 20 lbs. Small breed dogs have no problem using this unit, which gives them more room than other small or small medium sized window inserts. Unit has pet door in center with tempered safety glass on either side Note: These units can be installed very quickly with no tools and taken out just as conveniently. The Ideal Pet Window Insert has spring-loaded adjusting ends that give you approx. 5″ of range for fitting Weather stripping is provided so that you can make your unit fit tightly. The locking cat flap that is used in the insert is rugged and durable. You will never have to replace the flap. It features a 4 Way locking control. Will fit in a window sash groove upto 1″ wide. The height of the door is 6″ higher than the height of the flap.