Pet door that features inner telescoping frame that adapts to doors of 1/2 In. to 1-3/4 In. thickness. Includes high-quality aluminum construction and a clear flap to allow pet to see if slide isn t in place. Features tamper-proof mounting so that the door can t be removed from outside and a Thermo-Insulated lockout slide. Installation measurements is the opening you cut in the door to install. 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. null -