A Spring is an engineering component which when deflected by a force tends to return to its unloaded shape. Ideally the energy input to cause the deflection is usefully recovered.   Springs are mechanical components designed to store mechanical energy, working on the principle of flexible deformation of material.   Springs constitute one of the most widely used group of components in mechanical engineering.  When designing and/or selecting metal springs consideration should be given to material, manufacturing process, heat treatment, dynamic properties, elastic properties, strength, fatigue, shock, stability, surging etc etc.    Spring types include

Metal Springs...... Helical Compression Springs,  Helical Extension Springs,   Helical Torsion Springs.. Coil Springs,   Disc Springs,   Leaf Springs,   Spiral Springs

Other spring Types....Air Springs,   Elastomer Springs


Notes on spring design are found on the following linked pages..