For turning 4 different track or accessory circuits on and off. For example, power can be controlled in 4 storage sidings in 4 different track circuits. Unit comes with 8 sockets on the back and 2 sockets on the ends. All of the connections are for the new plugs from the 71400 sets. 8 appropriate plugs included. Dimensions 80 x 40 mm / 3-1/8" x 1-9/16".