Does anyone happen to know the size of the locking nut on the rear( swing arm ) I think that is what it is called . It has a plastic cap over it and is fastened to a large threaded rod that has an allen wrench center. I need to loosen it to adjust it slightly. I don't have many metric sockets that large and it would be easiest if someone could tell me instead of taking a guess till I get it right.
Thanks
Tim

 

Mine is a 17mm on the threaded rod and 19mm locknut