This shackle pendulum opening 1/2″ will save the cost and hassle of installing an S-hook. Use this to attach chains to swing hangers. Bolt pin has a tamper resistant head that requires an Allen wrench with a special hole to open and close. Can be used with any ductile iron or stamped steel hanger. It has a .51 ID oil light bearing and axle bolt with lock tight nut and accepts a 12mm bolt. The ID of the bearing is 13.1mm +/-0.05. Uses 12mm bolt and nut. Nut & bolt not included.