#1  As seen on this  20" wide Pontalba window box  a one inch wide strip with 1/4" diameter holes is attached to the back of the box 1/2" below the top of the horizontal side bars.  The advantage to this method is that all windows have footers which are usually made of wooden 2 x 4's or 2x6" that you can attach to with wood screws.

#2  The Bellflower window box is designed with a mounting strip 4 1/2" below the top of the horizontal side bars. This configuration allows the window box to be mounted around a protruding window sill.  It also lifts the flower box up so the flowers can be more easily seen from the inside of your house. (One word of caution ....if your windows open out it may cause a problem

#3 Note: tabs can be on the inside or outside of the window box frame.These side mounting brackets on this cathedral window box provides the option of installing your window box  at any height in relation to the window.  If you have any specific requirements  i.e.: spacing of holes for screws or height of mounting bar from top of box, just let is know and we will try to accommodate you.