Stranded-wire helical spring is a cylindrical helical spring rolled by a strand, which usually consists of 2 to 7 carbon steel wires of 0.4 to 3 mm in radius. The spring has two kinds of structures in accordance with whether it has central wire or not. The helical direction of the compression spring is opposite to that of the strand, while it has the same direction for the extension spring. Compared with conventional single helical springs, it has the unique characteristic of better damping and vibration re...