shanghai tonghui mechanical include Constant Force Spring, Constant Force Spring for Carbon Brush,Variable Force Spring,Power springs store and release rotational energy in the form of torque and are also known as clock or motor springs.Spiral-wound flat metal strips are available in a wide range of sizes and attachment methods for clock and mechanical motors,counterbalance mechanisms,reel returns and rewind devices (Main material is 304&316 stainless steel and SK4,SK5,62Si2MnA,carbon steel and etc).