1 Inch MS Windows Roller has end seals to protect rolling elements from dirt and contamination. Crowned rollers have a slight curve, which is invisible to the naked eye, to stay centered on surfaces that are not perfectly aligned and/or not perfectly flat. It a more modern style of window that can offer the ability for large opening expanses in certain situations. The rollers operate on wheels and a track very similar to that of a sliding door. 1 Inch MS Windows Roller is very efficient.