This is a very hefty planter.  It is large and well-constructed, but not what I'd call a "window" box, unless you've got very large-scale windows!  I'm using this on the railings I have around the periphery of my roof deck...it is perfect for the space.  The hooks don't hold the planter snug against the rail; they tilt a bit, but it still looks fine.  The product specifications say the minimum rail size is 0.75", but the brackets aren't adjustable to this small of width.  I like this so much, I've purchased 5!