A power take-off (PTO) is a spinning shaft, usually on a tractor or truck that can be used to provide power to an attachment or separate machine. It is designed to be easily connected and disconnected.
The PTO and its associated shafts and universal joints are a common cause of injury in farming and industry. When a piece of clothing, which can be as small as a single thread, touches a spinning part it can be pulled around the part. The clothing and the person wearing it are instantaneously pulled into the shaft resulting in loss of a limb or death. Some implements do use metal guards to try to keep a person from becoming entangled in a PTO shaft, but even with guards people need to exercise caution around PTO shafts when they are plugged into a tractor.
A shaft attached to the PTO.
Agricultural PTOs are standardized in dimensions and speed. The original specification calls for operation at 540 rpm. Two newer specifications, supporting higher power applications, operate at 1000 Rpm and differ in shaft size. The larger shaft has 21 splines, while the smaller has 20. All three types rotate clockwise when viewed from the implement.