This is a A-55SD 55SD Attachment Link PN: 55SDMain Description As Following : A-55SD 55SD Attachment Link P.N: 55SD Mounting hole size 15/64" Crossed From: 2221-24821 JOHN DAY Found in Section & Models : Chains/ Sprockets/ Pulleys/ Hubs > Steel Detachable Chains, (Miscellaneous) (UNDEFINED): SEVERAL Associated Items : New Also This is An Aftermarket Product And : Mounting hole size 15/64"