Different ways to tackle it. Can you hammer a smaller socket onto it? 12 point sockets work the best.
Or use a small drill to drill a hole in the nut right by the stud. Remove some meat the use a chisel to split the nut. These nuts are pretty soft you may just be able to chisel it. Can you double nut the stud anc back it out? I would start a regular 8mm nut and mig welf it to the stud wnd use a 13 mm socket to unthread the stud. Expect to replace the stud once your done regardless. Hammering anotger socket onto it is always the best when possible.
1 Like
Seconded, exactly what I was gonna say. 9mm 12pt ought to do it
Got it off with a chisel and a hammer, then I recut the threads so its all good now.
Thanks for the advice! 
Not my finest moment.
Always, ALWAYS use a 6 point 10mm socket on those lugs. A 12pt will mess them up faster and is more likely to strip them.
3 Likes
I use the smaller impact wrenches, like:
I immediately throw those horrible nuts in the trash and swap to the barrel nuts.
To each their own, I used to use the barrel nuts many years ago but much prefer the little 10mm nuts.
I use the titanium barrel nuts and will never go back.