Installation instruction: Circle top CloZures are attached with three screws.  Center the CloZure over your window and screw in the center screw.  When screwing into your sheetrock, you may run into only sheetrock, wood, or sheet metal.  You will not know what is behind the sheetrock until you begin your installation.  First assume that there is only sheetrock; do not use an electric drill.  Screw in slowly and do not over tighten.  If you run into a hard material, use an electric drill  before screwing in your CloZure.