SIZE: SOuter door frame size:19*19.7*2cm; inner door frame size16*15.7cm MOuter door frame size:19*19.7*5.3cm; inner door frame size16*15.7cm LOuter door frame size:25*23.5*5.3cm; inner door frame size19*18cm XL: Outer door frame size:25* 5.5*27.7cm; inner door frame size22*20cm 4 Way Locking Mode --- The pet door could be adjusted by the Red and Green switches with tabs to 4 modes: out only, in only, both in and out, and fully locked, easy control of your pet's in and out. High Quality --- Made of ABS material, weather-resistant, the surface is smooth and durable. It provides a fixed groove with snap tabs for weather-proof brush strip, firmly fix the brush strip. Even if the brush strip comes off, easy to put it back into the fixed groove. This greatly help the brush strip reduce noise, stop rain drop, wind or pest like mosquito to the most. Applicable scene --- It fits to being installed to interior doors, exterior doors, walls, windows, cupboards, glass, etc. Installation method: Required tools: electric drill, iron saw or electric saw, measuring ruler; Step1: first draw the size of the door cover with a piece of paper (there may be a few millimeters of error); Step 2: draw the drawing on the door and print it with pencil; Step 3: drill a hole in the four corners of the painted door with a drill, and then directly start digging if there is an electric saw; Step4: if it is a glass door, use a glass cutting tool to gently open it and fix it with glass glue; Step 5: the hole is cleaned. Now get a layer of wood skin to wrap around the hole for beauty; Step6: install the cat door. There are accessory screws and screw them with a screwdriver; STEP7: the screw port is also equipped with a screw cover. Press it, OK