Answer
'Spring Set' is the permanent loss of height that occurs when a spring is first compressed to a stress level exceeding the material's proportional limit. To account for this during assembly, springs are often designed with a free height $H_f$ slightly higher than the nominal value. During the 'Presidance' or 'Cold Setting' process, the manufacturer compresses the spring to its solid height. This induces beneficial residual stresses (autofrettage effect) that allow the spring to operate at higher loads in the future without further set. If a spring has not been pre-set, the assembly engineer must account for a $5-10\%$ drop in load after the first thermal or mechanical cycle. For $17-7PH$ CH900, pre-setting is essential to stabilize the spring for precision instrument applications.
