Ts: Lower Tensile Stress
	%Ts: Un-prestressed Limit
	%Ts: Overstressed Limit
	G x 10-6 : Modulus of Rigidity
	d: Wire Diameter
	D: Mean Diameter
	P: Load
	L: Length at Load
	k: Spring Rate
	Nd: Number of dead coils

	Lf: Free Length
	x: Deflection
	S: Stress
	%Ts: Percent of Lower Tensile Stress
	Kw: Wahl factor for 2% set point or fatigue
	C: Spring Index. The preferred range is 4-12
	Na: Number of active coils
	Nt: Total coils
	Ls: Solid Length
	Ps: Solid Load
	Ss: Solid Stress
	OD: Outside Diameter
	ID: Inside Diameter
	a: Helix Angle
	p: Pitch
	Lw: Wire Length

Spring Manufacturers Institute
Encyclopedia of Spring Design
Compression, Extension, Garter, and Torsion Springs