Trolley in production and life is widely used because of its low cost, easy to maintain, easy to use, light weight, difficulty in using motor vehicles in place to work, carrying lighter items very convenient short distance, carrying goods and labor, save time, and save money.

Unicycle in a narrow gangway, bridge and drive on the trail, parking maneuver, the dumping of goods is very convenient. Two-wheelers are commonly used to carry into items of hand pallet truck (also known as Tiger), a handcart and handling of bulk materials dump and so on. One of three-wheeled carts, four-wheeled trolley has two revolving castors can rotate around a vertical axis rotation (see figure revolving castors). This rotating casters in the running along with the direction of vehicle movement and automatically adjusts to the path of least resistance.