18mm steel shackle. Quite possible the strongest Ulock for bicycles in the World! This extreme bicycle U-lock handles the urban areas, college campuses and other high theft danger areas. The Kryptonite New York Fahgettaboudit has a 18 mm through-hardened Kryptonium Steel shackle which resists bolt cutters and leverage attacks. High security disc style cylinder. Hardened steel sleeve over crossbar for double security. Double deadbolt locking mechanism for extensive holding power. Center keyway defends against leverage attacks.