Nodding Donkey (also known as a “horsehead pump” or “pump jack”) provides the up/down motion (stroke) that powers a submersible pump in a borehole. The submersible pumps oil in a similar way to which a bicycle pump pumps air into a tyre. A motor, usually electric, turns a pair of cranks, which by their action raise and lower one end of a metal beam. The other end of the beam, which often has a curved end, is attached to a metal rod that moves up and down. The rod, which can be thousands of feet long, attaches to a pump deep in an oil well.