Frame Sides are not applicable to an Inside Mount - Direct Mount since this mounting method does not have frames. However, for all other mounting methods, you can choose the sides of the window that you want to have frames. You can have different windows with different frame sides. For example, if you have a window with a protruding window sill, you may choose frame sides of "Three". If a window in the next room does not have a protruding window sill, you may choose frame sides of "Four".