(1) the strength calculation formula

 Type, the K coefficient of curvature,

F load;
C for the spring index C (also called wrapping), C = D2 / d;
T for spring material allowable torsional stress. Thus can calculate spring wire diameter d.

(2) the stiffness calculation formula

Type, n is the number of turns of the spring;
Shear modulus G for spring;

Lambda is spring deformation;
D2 in spring coil diameter;
Like the previous other symbolic significance.

(3) the stability calculation formula
In order to limit the spring load F less than buckling critical load Fcr. Generally take F = Fcr/(2 ~ 2.5), the critical load can be press type calculation
Fcr = CBkH0
Type in the CB for the unstable factor

Note: 1 - both ends fixed; 2 - fixed at one end; 3 - free rotation at both ends