A combination of control device and special bending design usually seen in Water Boiler Elements installed in manually filled vessels. One small section of element sheath above the rest of the formed element this is attached mechanically or by welding to a Bi-metalic Cut-out Thermostat.
This Thermostat can be manual or auto resettable. It is not designed to prevent failure if the entire element is exposed whilst energised. If possible this should be used with additional devices to ensure the elements are completely immersed.