You actually use the orange tabs to hold it in. Take the tabs off and cut a rectangle in the surface you are mounting it in. Try to make the rectangle cut out so STC 1000 just barely slides in...make it a tight fit. Push it in all the way until the flange stops it. Then just reinstall the orange clips from the inside, click them forward as far as you can sandwiching the plate in between the flange and the clips. Piece of cake!