2006 Volvo VNL alternator nut..

This is going to seem like a stupid question but anybody know what's the nut size at the alternator negative battery cable connection on 2006 volvo vnl? I had a mechanic over trying to figure out what my electrical problems were and he disconnected that negative cable from the alternator and did not put it back on and the nut ended up falling in the grass so can't find it. tried 1/4 size standard nut and the metric equivalent with no luck.. it will screw on a bit and then stop. there were 2 nuts on it to start out with so i had the one to compare with and it still screws on fine just in case your thinking the threads on it are messed up keeping me from getting any nut on it. i know from the pic the threads look chewed up and they are but like i said the original nut still screws on fine.. called up volvo to ask them what it was and they couldn't figure it out. said i would need to bring them the alternator and they'd figure it out from there. said every volvo's different.. what a freaking mess. it's a alternator nut for God's sake's.. anyways any help would be appreciated.

 

I tried the m6 (1/4 standard equivalent) but it didn't work..

 

do you have any idea were I would get a bolt of this thread pitch assuming this is a thread pitch different from a standard 6mm nut thread pitch? From what I can tell auto zone has metric and standard nuts but I don't "think" they have different thread pitch's but could be wrong. They have a fastenal store in the waco area close to were I live that would probably carry different pitch sizes I don't know just thinking out load at this point.. what kind of company puts a nut on an alternator that you can't find anywhere? i'm thinking i need to pass this volvo on as soon as i get the chance lol..

 

Good point, I think it's a delco. I'll try to look them up.