The overrunning clutch, also known as a one-way clutch or sprag clutch, is the mechanical device. Its primary function is to ensure one-way torque transmission while allowing free rotation in the opposite direction. It’s widely used in various equipment, including the power take-off (PTO) shafts of tractors.

Typically on a trailer, the PTO shaft transfers power from the tractor’s engine to various implements, and this transmission is one-way. However, the implement sometimes may have its own power source capable of driving the PTO shaft in reverse. That’s undeniably dangerous. To avoid this situation, a overrunning clutch is usually used.

The overrunning clutch typically consists of two main parts: inner race + outer race. They both equipped with sprags or rollers. The inner race connects to the PTO shaft, while the outer race connects to the implement. When torque’s applied in the driving direction, the sprags or rollers engage between the races, enabling power transmission from the PTO shaft to the implement. Conversely, when torque is applied in the reverse direction, the sprags or rollers disengage, allowing the PTO shaft to rotate freely while preventing the implement from driving it. So this is the working principle of an overrunning clutch.