The built-in leg of the semi-trailer is the supporting device of the trailer. Its function is to support the ground when the tractor is unhooked from the trailer, to withstand the load of the front half of the semi-trailer, and to turn the handle to raise and lower the support device by two speeds, high speed. For no-load, low-speed gears are used for heavy loads. The built-in legs are gears inside the square legs of the legs, making the legs lighter.
