Extension Springs Meaning of Symbols The symbols used for extension spring design are shown in Table 1 below. The values of the transverse elastic modulus (G) are based on Table 2. Table 1. Symbols and units used in calculations Symbol Meaning of Symbol Unit d Material diameter mm D Coil center diameter mm Hf Free length mm Na Number of active coils — P Load applied to the spring N δ Spring deflection mm k Spring constant N/mm Pi Initial tension τi Initial stress mm M Torsion moment, bending moment N/mm σ Tensile stress N/mm2 τ0 Uncorrected shear stress N/mm2 τ Corrected shear stress N/mm2 κ Stress correction factor — … Continue reading Extension Springs: Calculation Formulas