The plastic edges are cheaply made for the cost of the product, and uneven. They are supposed to fit into the grooves of the rail, but some were loose and some were very tight - almost sealed. I wasn't even sure that the edges were made of plastic, immovable, and wouldn't slide in or out until I attempted to work one rail into a tight edge and the edge broke off (see picture). Lesson learned. Why this company would make their product this way and charge nearly $40 for it, is beyond me.