ASNU25 One Way Clutch One Clutch ASNU25 = NFS25 ASNU25 is a one-way clutch. One way Sprag/Clutch Freewheel and also called as Backstops. ASNU25 is used in any applications 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.