ThermoPlastic pet door features inner telescoping frame that adapts to doors of 1-1/4 In. to 2 In. thickness. Includes impact resistant super-strong thermoplastic， clear vinyl flap with patented edges won't warp from use or extreme temperatures， and floating bottom threshold for perfect seal. Lock-out slide keeps pet out of mischief when unsupervised. Features tamper-proof mounting so the door cannot be removed from outside. Easy installation - average installation time is 20 minutes. How to select the right pet door: Step 1: Measure your pet from the top of the shoulders to the chest， just behind the front legs. Step 2: Determine your pet's weight. Step 3: Select the correct door size based on your pet's measurements and weight.