Music wire, alloy spring steel, stainless steel etc.
Outside Diameter, Inside Diameter, Wire Diameter, Free Length and Extended Length
The Free Length is the length of a spring in the unloaded position (measured from inside the end loops).
The Extended Length is the length at full rated extension.
Zinc/ Gold irridite/ Passivated/ Black Oxide/None
The hook types include Machine Hooks, Cross Over Center Hooks, Side Hooks, Extended Hooks, and Double Loop Hooks.
Extension springs are used in trampolines, push and pull levers, rocking horses, screen doors, farm machinery, and anywhere else extended force is necessary.