Endura Flap Pet Door for Vinyl Sliding Glass Doors | Dual-Flap Extreme Weather Design | Insulated, Energy-Efficient Dog Door with Locking Security | White, Medium Flap, 74.75"-77.75" Slider Height SEAMLESS INSTALL: the Endura Flap pet door for vinyl sliders is designed for 'U' shaped tracks of at least 1-1/2" width; engineered for optimal insulation and energy efficiency to provide freedom for your pet while preserving your energy bills; small flap measures 8" x 15" and is suitable for pets up to 21" tall MAXIMUM ENERGY EFFICIENCY: enhance your home's energy efficiency with our insulated pet door, featuring LoE glass to reduce UV rays and infrared light; the durable and flexible flap remains functional even in -40 degree temperatures, providing your pet with easy access to the outdoors EASY INSTALLATION: experience how simple it is to install and remove our pet door with the adjustable top and spring-loaded design, allowing for a fast, secure fit in your sliding glass door track; the white vinyl frame complements most interior designs and provides a stylish addition to your home FOUR-SEASON PERFORMANCE: protect your home from harsh weather with our weather-resistant pet door, capable of withstanding winds up to 50 mph; the insulated flap ensures your home stays comfortable during winter, spring, summer, and fall, keeping the elements at bay SECURITY PEACE OF MIND: includes a secure locking cover, as strong as 1/16" sheet steel, providing added security and control when the pet door is not in use; the Endura Flap pet door is built to last.