Features: 1. Easy to install, simple and generous. 2. The quality is very good, using ABS material (a very good kind of plastic) 3. Large, relatively large size, suitable for a lot of fat cats. 4. Four major functions: (1) No entry and no exit (completely closed) (2) Can go in and out (completely open) (3) Only in but not out (4) Only going out but not in Installation method: Tools needed: electric drill, iron saw or electric saw, measuring ruler; Step1: First use a piece of paper to draw the size of the door cover (there may be a few millimeters error); Step2: Finish the drawing and mark it on the door, and draw the seal with a pencil; Step3: Use a drill to drill a hole in the four corners of the painted door, and then start to dig the hole directly if there is a chainsaw; Step4: If it is a glass door, use a glass scribing tool to gently cut it open and fix it with glass glue; Step5: The hole is cleaned up, now first get a layer of wooden leather to wrap around the hole, for the sake of beauty; Step6: Install the cat door, there are accessory screws, and screw them on with a screwdriver; Step7: The screw port is also equipped with a screw cover, press it, OK. Package: 1 * Pet Door Note: 1. Due to the different monitor and light effect, the actual color of the item might be slightly different from the color showed on the pictures. 2. Please allow 1-3cm measuring deviation due to manual measurement. 3. S size is thinner than other sizes!! If you have other questions, you can contact us at any time, thank you.