A drawbar is a piece of equipment which is used as a coupling between an engine and the load it pulls. Drawbars do not transfer the weight of the load to the engine, but rather act as a point of attachment so that a load can be hooked onto a trailer, truck, tractor, or similar type of engine. The load is balanced on wheels and supporting struts of its own.
A classic example of a drawbar can be seen on farm equipment. A tractor is equipped with a drawbar so that it can haul different types of farm implements such as plows, harrows, cultivators, reapers, and so forth. In addition, most tractors can pull simple trailers which may be loaded with supplies or animals; anyone who has gone on a hayride, a popular fall activity in some areas of the world, has probably been pulled in a trailer attached to a tractor with a drawbar.
Another example can be seen on railroads. On many trains, only one car, the locomotive, has an engine. All of the other cars are supplied with energy to move by being attached to the engine and each other with draw bars. Some locomotives have tremendous pulling power and can handle extremely long and heavy trains, while in other cases, a second locomotive needs to be attached to supply additional energy, especially if the train needs to travel up a grade.
Large trucks can also utilize this type of coupling. Drawbars can be used for towing other vehicles, including boats on trailers, and for attaching a trailer to a truck or car. Some trucks are manufactured with a drawbar and accessories installed, while in other cases it is necessary to add them. The drawbar usually comes with a load rating which is determined in part by the power of the engine it is attached to, and by the materials it is made from.
A mechanic can fit a vehicle with a drawbar or repair an existing one in the event that it is required. It is advisable to avoid loads which exceed the capacity of the drawbar, as the bar could fail during hauling and at high speeds this could be catastrophic. If the rating is not clear, a mechanic can be consulted for advice, and sometimes it's possible to find a drawbar calculator, with the user inputting variables such as the type of vehicle and drawbar model and the calculator returning a recommended load capacity.