It is a dolly that provides the advantage of a 3 Point load system while being a part of 4-Point Rigging System. In other words, the dolly which is the front steering portion of the rigging system has one handle that orients 2 separate machinery skates. The tandem connection is what maintains the machinery skates in perfect parallel. When you move the handle in one direction the 2 machinery skates steer in sync like the 2 wheels of a car.