Lever 2, turning about fixed axis A, has two screws, a and b, which serve to adjust the angles of rotation of the links of the mechanism. Lever 3 turns about fixed axis B. Force is applied by spring 4 to hold the mechanism in the closed position. Screw a is in contact with rod 1 which is immersed in the medium being heated. As the temperature is raised rod 1 expands, actuating screw a of lever 2. This turns lever 2 about axis A and screw b turns lever 3 about axis B so that the lower end of lever 3 swings from the contact to stop d, thereby opening the circuit that heats the medium.
$360$SL,SE$