Inside Mount: LazBlinds Zebra Blinds's actual rail width is 1/8 inch narrower than the labeled size for a perfect fit inside your window frame. If your window is 20 inches wide, simply order the 20 inch blind for a smooth, custom look, no need to calculate deductions Outside Mount: For outside mount, we recommend choosing a blind width that is 2-4 inches wider than your window's outer frame.
