The design of extension springs needs to take into account the initial tension which must be overcome as well as the stress characteristics of the various spring hook ends which might be used. The paragraphs below summarize these considerations.

Extension Springs

About 10 percent of all springs made by many companies are extension springs, and they frequently cause trouble because insufficient consideration is given to stress due to initial tension, stress and deflection of hooks, special manufacturing methods, secondary operations and overstretching at assembly.