For the most part, springs are manufactured of spring steel wire of the maximum strength category with a special surface finish. The working temperature range for these springs between -30 °C and +120 °C also determines the operating temperature range for the complete spring contact probes. High-strength stainless steel wire is used with higher temperatures up to +250 °C and when increased demands are made of corrosion protection. However, with this wire, it is not possible to achieve such high strength or spring force values as with spring steel wire.
Normally, gold is used as a surface coating because it reduces wear and improves the contact characteristics. The coating is applied in such a way that the structural characteristics of the high-strength spring material are affected as little as possible. In special cases, the springs are silver-coated (improved conductivity) or stainless steel springs are not given an additional coating.
The rated spring force of the spring contact probes refers to the working travel, which, as a rule, is 4/5ths of the maximum permitted plunger stroke travel.