The circuitry signals when the ice thickness is just right and forces the harvest process. The thermistor resides in an enclosed well called an eyelet. See Figure 1. Even though small, the eyelet must still be mechanically strong enough and meet all NSF requirements. Because of its small surface area, it is very hard for lime to build up, thus making it less of a factor in the overall operation.
Copper is easy to manufacture and inexpensive, while nickel plating makes it abrasion resistant.
The eyelet material must have a high conductivity coefficient and not insulate the internal thermistor from delaying its sensing of what is happening near the eyelet. The eyelet is pressed into a carrier and sealed. See Figure 2. The carrier is designed with a setscrew to allow adjustment of the separation between the sensor and the ice-forming surface. The setscrew must be located on the carrier to match up with one of the ribs on the cuber to insure that the same exact gap is set at the beginning of each ice-making cycle.