Petsafe Big Cat Flap Guide D'installation page 8

Install the cat flap
1
Insert the interior frame into the opening on the interior side
of the door.
Have a helper hold it for you, or tape it in place while you go
to the exterior side of the door to fit the exterior frame.
8
2
Place the exterior frame on the exterior side of the door,
fitting it over the tunnel of the interior frame.
Holding both frames in place, insert screws through the holes
in the exterior frame, through the cut opening, and into the
holes on the back of the interior frame. If your door is:
• Between 25 mm (1 inch) and 32 mm (1 1/4 inches) thick,
use the 57 mm (2 1/4-inch) screws.
• Between 32 mm (1 1/4 inches) and 51 mm (2 inches) thick,
use the 70 mm (2 3/4-inch) screws.
Make sure the cat flap is level in the opening and then
tighten the screws with a manual Phillips screwdriver. Do not
over-tighten.