[krygny]

With the right tool, the size of your nuts doesn't matter:

<img src="http://gemini.tntech.edu/~slc3675/me361/mechlib/vgrip.jpg" alt="Vice Grips" />

 

[krygny]

If that isn't a metric vice grip you could screw up the oil drain bolt.....

I don't think that matters, as long you use a right-handed one to loosen it and a left-handed one to tighten it.