Stern service means fast continuous loading where ratio of smallest to utmost load (or stress) is one -half or less, as in automotive valve springs.
Average services include similar stress range as in severe service but by simply irregular process, as in engine governor springs and automobile suspension springs. Light service includes springs subjected to loads that are static or very infrequently varied, as in safety valve springs.
The springs are generally made as of oil-tempered carbon steel wires contain 0.60 to 0.70 per cent carbon and 0.60 to 1.0 per cent manganese. Music wire is use for little springs. Non-ferrous materials similar to phosphor bronze, monel metal, beryllium copper, brass and so on., can be use in special cases to amplify fatigue resistance, temperature resistance and corrosion resistance.