We are leading manufacturer of Variable Transformer Spare Parts, which are remarkably similar. The largest parts in the transformer consist of the winding coils and a sliding brush. The knob on the device offers a way of insulating the user from the voltage going through the device, allowing them to adjust the surface area of the brush that is actually touching the coil. A variable transformer will also restrain parts that are designed merely for safety's sake. The largest parts however, are the coil and the brush, the latter of which basically takes the position of the secondary coil in a usual two coil transformer.