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An interior mount involves hanging the shades inside of the window frame. This is a good option if your window frames are deeper than 3–4 inches (7.6–10.2 cm). When you use an interior mounting style, you'll attach the Roman shades to the downward-facing surface on the upper interior of the window frame (often called the frame's “ceiling”).  Mounting your Roman shades in the interior style is a good option if you have strong window frames that can bear the weight of the heavy shades. An interior mount also gives a more finished look, and it doesn't cover up the top of the window-frame molding. As a result of old age or poor construction, window frames often have a slightly uneven “ceiling.” Use a level to test whether or not the frame is even. Hold the level up against the frame's “ceiling,” and make sure that the small bubble is clearly in the middle of the marked section on the tool. If you're using an exterior mount, you won't need to check that the frame itself is level, since you won't be attaching the shade to the frame. If your frame ceiling is not level, you will need to insert a couple small shims to even it out. Begin by using a hammer to pry off the molding from around the edges of your window frame. Then, place the tapered end of a shim between the window frame and the wall on the low (sagging) end of the frame. Lightly tap the shim in by at least 1⁄2 in (1.3 cm) to raise that side of the frame. Use your level to see if the frame is evened out after every 3-4 hammer taps.  A shim is a thin, angled piece of wood that will make the ceiling level when nailed in place. You can purchase shims at any hardware store or home-improvement store. Once the window frame is level, snap off the ends of the shims that are sticking out past the end of the frame. Then, use your hammer to reattach the molding around the window frame. You should be able to stick the nails back in the same holds that you pried them out of earlier. The shade's headrail is the long top metal piece of the shade, from which the fabric shades themselves descend. Measuring the headrail will help you find the location where you'll mount the brackets that hold up the headrail. Hook the metal prong of your tape measure and extend the tape to the far end of the headrail. Then use the tape measure to find the width of the interior of your window frames. Note that if the headrail is longer than the window frame is wide, you must use an exterior mount. Extend your tape measure to the exact length of the headrail, and hold it up inside of the window frame, against the frame's “ceiling.” Lightly mark the endpoints of the headrail. Then, measure in 3 inches (7.6 cm) on either side of the headrail's endpoints. Mark these 2 spots with a pencil. These markings will indicate where you'll hang the 2 brackets.  For example, say that the headrail measures 24 inches (61 cm) long. To find the locations for the brackets, measure in 3 inches (7.6 cm) on either side. So, you'll place 1 mark at the 3 in (7.6 cm) point and another at the 21 in (53 cm) point. Once you've marked the locations for the brackets, you can erase the light markings that indicated the endpoints of the headrail. Pick up 1 of the C-shaped metal brackets and hold it in place on top of the pencil markings you just drew. The bracket should have 2 screw holes. Use your pencil to place a small “X” in each of the holes. You'll use these markings to insert the screws that hold the brackets in place. Then, repeat the process, holding the bracket up in the second bracket location that you marked earlier. Use a pencil to marking the 2 locations where you'll insert screws to hold the second bracket in place. Insert a 1⁄8 in (0.32 cm) drill bit into your electric drill. Hold the drill vertically with the bit pointing up, so that the tip touches 1 of the “X” spots you just marked. Drill a pilot hole in each of the 4 marked locations. Drill each pilot hole 1 inch (2.5 cm) deep. If you didn't drill pilot holes, the screws used to hold up the brackets would splinter the wood. Place each bracket on the marked location on the wall. Line up the brackets with the pilot holes that you just drilled in the window frame and slip the 2 screws through the holes in the brackets. Use a screwdriver to screw them in place.  Use the brackets and screws that came with your Roman shades for installation. This makes installation more convenient and cheaper than if you had to buy new screws from a hardware store. Different brands of Roman shades may have slightly different installation methods. If you get confused, follow the specific directions that came with yours. Roman shades are outfitted with twin brackets that click into place with the brackets you've attached to the wall. To install your shades, slide the top of the shades forward until the two brackets click into place. Make sure that the headrail is centered over the window. At this point, the shades should be secured in the frame. If you need to remove them at a later date, just give a sharp tug in the direction opposite the way you slid them into position. Lift up the Roman shade so that you're looking beneath it at the bottom of the brackets. Pick up the short 2 in (5.1 cm) head screws that came with the Roman shade kit and thread them into visible hole in each of the 2 brackets. Using your screwdriver again, tighten the head screw firmly into headrail. These head screws will prevent the headrail from popping out of the bracket if you give the cord too sharp of a tug.

Summary:
Choose an interior mount if you have sturdy, square window frames. Check if the window frame is level before mounting the brackets. Shim the frame if it's not level so your Roman shades hang evenly. Measure the shade's headrail with a tape measure. Mark the 2 bracket locations on the frame with a pencil. Place an “X” on the 2 screw locations for each of the brackets. Drill pilot holes upward into the “ceiling” of the window frame. Screw the brackets into the pilot holes with a screwdriver. Slide the shades into place in the mounted brackets to secure them. Drive a head screw into each end bracket to secure the shade.