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A power take-off or power takeoff is one of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine.
Most commonly, it is a splined drive shaft installed on a tractor or truck allowing implements with mating fittings to be powered directly by the engine.
Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a drive shaft and bolted joint to transmit power to a secondary implement or accessory. In the case of a marine application, such shafts may be used to power fire pumps.
In aircraft applications, such an accessory drive may be used in conjunction with a constant speed drive. Jet aircraft have four types of PTO units: internal gearbox, external gearbox, radial drive shaft, and bleed air, which are used to power engine accessories. In some cases, aircraft power take-off systems also provide for putting power into the engine during engine start. See also Coffman starter.