Material: high carbon spring steel, spring steel, stainless steel, alloy steel Compression Spring, Extension Spring : Wire Diameter: 0.2-40.0mm Torsion spring wire diameter :0.2-35mm Surface Finish: black , Zinc, Nickel, silver, golden, tin, powder coating, shot pin Applications: Automotive, medical device, agricultural machinery ,electronics, toy, electric power distribution. Extension spring hook include Germany hook, British hook, Side hook We can customize special design of springs based on your requirement.