These heavy duty garage door rollers are constructed of steel wheels and rods and they include steel ball bearings. The wheels measure 1-13/16 inches in diameter, the shafts are 6-13/16 inches long and measure 7/16 inches in diameter. Each roller is equipped with a steel inner race and factory lubricated steel ball bearings. Garage door rollers like these are used on side by side hinge placements for added strength.