Atlas O 6929 Atlas O(R) Heavy Duty SelectorThis component enables the operation and control of two trains at the same time when they are running conventionally. Features four single pole, double throw switches that allow two cab operation of four blocks. It can also be used as area selectors for four cab operation. The heavy duty design is compatible with higher amperage AC DC command control systems and all large scale trains. May be ganged together in any number to control additional blocks