The M 4 Vigitherme is made up of a stainless steel case and a nylon body carrying the connecting screw terminals. The parts under tension are insulated from the ground of the apparatus. The bi-metallic disc is located at the bottom of the stainless steel case which then constitutes the portion sensitive to temperature.
A M 4 B version that does not return to initial state by cooling is also available. To reactivate it, it is necessary to press the red button located in the middle.