No idea, Yamaha are weird when it comes to rear brakes, they don't seem to settle on any design. They had discs, then drums, then hydraulic discs, then drums again, then discs, then wet brakes inside the rear diff, then back to discs, so if they went back to drums for 2014, I haven't come across them. A picture of what you have may help.

 

 

That is a 1 time use nut buy a new one. That nut takes the place of a tab washer after torqueing the nut you take a punch and bend it down in so the nut cant back off. To get it off you can use an impact or bend it out and remove

 

 

you bet good luck they can be a pain without an impact.