CSK40 One-way (clutch) Bearing The CSK series is a one-way (clutch) bearing.One way Bearing Sprag/Clutch Freewheel and also called as Backstops. The one-way bearings are used in any application that requires one direction rotation, such as mining, hydraulic, textile, printing and washing machines, conveyor systems that carry products to a higher level should not be reversed because of gravity during any power shortage.