Screen door for cats and small pets. If you already have a screen or mesh protective door or plan to buy one, then this pet door is what you need. It is quite sturdy and does not fall easily. With sliding locks on both sides to prevent your pets from walking freely. You can install this pet door on indoor/outdoor screen doors, windows, and any other thin structures. It cannot be used on very thick wooden doors, iron/aluminum doors, and walls. Screws and nuts are provided for easy installation.