extension spring 1.Widely used in automobiles,motorcycles,amusement park ... steel,stainless steel 1)The Wire Diameter of this extension spring: 1.00 mm-20.00 mm;2)Raw Mterials ... of this extension springs:stainles steel 302, hign carbon steel, music wire ... plating, chrome plating, zinc plating,etc;4)This Extension Springs are produced by CNC spring's machines;5)High Quality.