Die springs (ISO 10243) have been especially designed and manufactured for applications where great spring force is required in a limited space. Special material properties allow a large number of spring load variations. The springs are divided into seven (7) strength classes and colour-coded according to the strength class. The spring surfaces are colour code-painted to indicate the strength of the spring, not for protection purposes.
More information on die springs: https://www.meconet.net/tyokalujouset/