STACO variable transformer 

Designed to protect the transformer from physical abuse, chemical spills, and other hazards. Overvoltage output is available when knob is turned fully clockwise. Meter accuracy is ±3%. 50/60 Hz.

Suitable for controlling electric heating elements, lights, electric motor speed, or power. Output voltage controlled by a large slip-resistant knob with the output increasing linearly as the knob is turned clockwise. All models include a three-conductor grounded line cord, matching receptacle, switch, pilot lamp, and fuse.