Color Light Block Signal. Gauge: H0. This is a simple block signal for use on rail lines away from station areas. The signal aspects change from Hp0 (red) to Hp1 (green). Track current can be controlled by means of the 72751 control box. Maintenance-free LEDs. Height without base approximately 78 mm / 3-1/16". A suitable control box is 72751. The 74391 signal cannot be operated with other controllers! Can also be used with the m84 decoder (60841) in digital operation.