Because the bearing there needs not only lubrication but also cooling. SKF CircOil systems lubricate and cool at the same time and remove dirt, water, and air particles from the oil. SKF explicitly names roll-stand drive gearboxes, converter drives, gears, and backup-roll plain bearings as applications, and positions the system for applications above 80 °C in and around the bearing. The reservoir volume is also only about a third of that of a conventional system.