Rear chain double half link/ offset link / cranked link, 110054, narrow 520, 5/8 inch x 1/4 inch Renolds Synergy. Double offset link used to make an odd number of links in the chain. NOTE: This half link will only fit a Renolds 110054 chain. A generic cheap 520 chain has thicker side plates and longer pins. The original chain fitted to Nortons, Triumph, Velocette, Ariel original number 110054 GY10B1NAS30I Renold Synergy chain lasts up to 6 times the life of other brands see Renold synergy website