torsion spring extension spring hook include germany hook, british hook, side hook. we can customize special design of springs based on your requirement. 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.