D.I.D.'s 520MX series chain is a non O-ring chain with a higher tensile strength for maximum performance and is ideal for muddy conditions. D.I.D.'s SDH high-tech pin treatment forms an extremely hard chromium carbide layer on the pin's surface while maintaining a softer inner core. SDH treated pins have extreme impact strength while adding outstanding shock absorption. The SDH process creates a chain with superior wear resistance and outstanding anti-oxidation properties.