Tamper-proof (Pre-set) Thermostat FTO 011: Contact breaker/NC (red casing) for regulating heaters or for switching signal devices when temperature has fallen below the minimum value. The contact opens when  temperature is rising. 

Tamper-proof (Pre-set) Thermostat FTS 011: Contact maker/NO (blue casing) for regulating filter fans, heat exchangers, cooling devices or for switching signal devices when temperature limit has been exceeded. The contact closes when temperaure is rising.