A cylindrical helically coiled compression spring made of a length of wire or rod having a circular cross section, the spring having interior windings providing the main spring action and end winding portions at least one of which is arranged to be supported against a spring disc, and the wire rod being...http://www.google.com/patents/US4377280?utm_source=gb-gplus-sharePatent US4377280 - Cylindrical helical compression spring
