Just fixed a flat...

I just took the wheel off to get the tire fixed and noticed one of the lug nuts doesn't even hold on the rim at all. It just screws all the way back to the end of the stud! It's been like that for a while I'm guessing and doesn't seem to be a problem. Is it though? Any help would be great. Thanks.

All nuts must be seated on the rim. There is some redundancy for having 5 lug nuts. Often you can drive around on 4 without incident ( I did see a car with only 2 of 5 nuts on once. ) but it's not recommended at all.

Take a look at the offending stud. Is it longer than the others? Are the threads damaged? If yes, then replace it. Often you can knock the old one out with a hammer and install a new one. Usually the process of tightening up a lug nut on the new one will seat it.

Also, have a look at the nut as well. Is is shorter than the others, or is there something blocking it inside or has damaged threads?

It's just someone must have lost the lug nut that's supposed to go there and just put a regular nut in its place. It's not that big of a deal and I'll try to get a new lug nut when I can find one. The regular nut just goes to the end of the stud on doesn't flare out like the others.