Operating principle

Coiling of the thermostatic bimetal achieves greater “active length” within a small space, thus maximizing the possible displacement. One end of the spiral /helical coil is permanently fixed .the loose end describes a rotary path in response to a change in temperature..

The choice between a spiral or a helical coil depends on the intended application.

Spirals are preferred for measuring ambient temperatures (room temperature, sauna thermometer).