The guide roller is a safety device designed to keep the door from slamming into a wall when the door is opened all the way. The 54 guide roller specifically works with sliding box track hardware. The wheel portion of the guide roller is made of high impact nylon, measuring 2 1/2″ in diameter. The wheel has a steel frame, 6″ long x 2 3/4″ high x 2″ wide. Fasteners are not included. Richard-Wilcox recommends that you purchase a guide roller strip (#0647.00274) alongside the guide roller.