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RANGER says:

RANGER wall-mounted doors are engineered to install and trim out like much like a window. This allows the pet door to be used in walls of virtually any thickness. It also allows the pet door to be installed in a code-compliant manner. This is different from other, less energy efficient pet doors.

The pet door frame itself is 3-1/2” thick. Like windows, which are often much thinner, the pet door is installed from the exterior side, shimmed to plumb and square, and fastened in place. After weather sealing around the perimeter, any remaining wall cavity can be trimmed out with jamb extensions or a drywall wrap. Most people choose trim that matches their window trim.