Lost a bolt on the rear hub

[rex]

I lost the top nut off the rear hub.

Any idea what size it is?

http://216.37.204.206/alba/Yamaha_OEM/YamahaATV.asp?Type=13&A=212&B=32

It's Part 31.

???

 

[warriorspeed350]

17mm

 

[imtarnished]

Yoiu can take the threaded rod that it was attached to to a local hardware store, or home improvement center, and head to their hardware/nuts and bolts section, and they should have a little panel you can thread the rod into to get the thread count per inch, and the exact size. Not just the size of the wrench needed.
Other than that it's the only way I can help, good luck.
~Bill