disc 24 is still in the dished upward position referring now to fig4 after sufficient heat is radiated by and or conducted from heater 15 to various parts of the roller the thermal energy is transferred by conduction to both the heavy end 28 of the roller body where it is stored and to the roller end cap member 32 which is positioned to transfer some heat to bimetallic disc 24 when disc 24 reaches its preset avalanche point at a predetermined temperature it abruptly reverses its position from concave to convex thereby providing head space on the new concave side of disc 24 this permits pin 25 to rise axially through the upward force exerted by contact 14 thereby opening contacts 10 and 14 and deenergizing heater 15 at this point by the audible click of disc 24 or by observing the extinguishing of an optional pilot light connected in parallel with the heater not shown the user receives a signal to withdraw the roller which is ready for use in the event that the roller is left in the hair setter for a period until sufficient cooling takes place the system will automatically recycle reheating the roller after the roller is installed in the user 39 s hair latent heat stored in the heavy end 28 of the roller transfers to the relatively thin cylindrical wall of the roller to replace heat lost through conduction to the hair thus imparting additional useful hair setting heat referring to fig6 a.