TorsionSprings Meaning of Symbols The symbols used for spring design are shown in Table 1 below. The values of the longitudinal elastic modulus (E) are based on Table 2. Table 1. Symbols and units used in calculations Symbol Meaning Unit d Material diameter mm Di Coil inner diameter mm D0 Coil outer diameter mm D Coil average diameter　D=( Di + D0)/2 mm ΔD Reduction in coil average diameter with load applied mm N Number of coils — v Poisson’s ratio of materials（0.3) — c Spring index　c=D/d — E Longitudinal elastic modulus GpaまたはN/mm2 l Second moment of area Z Section modulus P(P1, P2) Load (Force) applied to the spring N M … Continue reading Torsion Springs: Calculation Formulas