This bizarre piece of hardware is a series circuit combined pulley and automatic cut out for carbon arc street lamps. The cylinders on the top are intended to take wood pins for mounting two glass insulators. How these devices work is that you lower the lamp from the pole arm or structure on a rope and as you lower the lamp this device disconnects the lamp electrically and mechanically from the line and then reconnects it when it is raised back into position. Inside the upper portion there is a contact switch that automatically closes and short circuits the series pole line as the lamp is lowered. I wish I had the upper portion of one of these.