Compressed Length The length of the spring after operating force has been applied. The compressed length is computed by subtracting the initial compression and the operating travel from the free length. Deflection Amount of change in spring length when force is applied. Elastic Limit The maximum compression stress that a die spring can endure without taking permanent set. Free Length The length of a die spring before it is subject to any operating force or load. Hole Diameter This identifies the outside diameter of the die spring. Producto springs are available in eight different hole sizes matched to standard drill sizes. Each spring is made to fit in the hole so the O.D. of the spring is actually less than the hole diameter. Load This is force built up by compressing the spring. Load is expressed in terms of total pounds which is the load on the spring per a specified unit of deflection (i.e. /10 in.) Load is also directly related to stress. As the spring is compressed, load is generated and stress on the coils increases. Operating Travel The distance which is subtracted from the spring length after operating force has been applied. Permanent Set This happens when the elastic limits are exceed and the spring does not return to its original length when the load is released. Preload The distance the free length of the die spring is reduced by the pressure of the assembled tool. Remove Set The manufacturing process of closing a compression spring to solid to eliminate load loss in operation. Rod Diameter This is a nominal identification of the inside diameter of the die spring. Producto die springs are available in eight rod sizes matched to standard stripper bolts. Each spring is designed to fit over the rod so the I.D. of the spring is greater than the rod diameter. Solid Height The length of a spring under sufficient load to bring all coils into contact with each other. Stress In a spring this describes the internal force that resists deflection under load. This force is equal to, and in opposite direction to the external load. Stress is expressed in thousands of pounds per square inch of sectional area.