stripped cylinder bolt

if theres room you can do the two nuts tightened together above the stripped nut and try to back the whole stud out. first you tighten the two good nuts together nice and tight then you put your wrech on the bottom good nut and try to losen it. that should work if there is enough room to get two nuts on above the stripped one.
 
clearly to you maybe. we can't see your quad from here. it was just a suggestion. you could also try to file down two flat sides to fit the next size wrech on there. or try hammering a standard size wrench on there like suggested before