Re: Help an idiot out.
If you're at all concerned that the smallest wrench in the small wrench bundle at your hardware store is still too big, try taking it to guitar shop and let the tech try his wrenches until he finds one that fits. At worst, you'll now know what size. At best, he may just give it to you. During my brief stint in MI sales, we did that kind of stuff all the time, without charge.
Also, while adjusting the saddle is probably the easiest potential fix, you should also be prepared to check that the nut slot hasn't been cut, or worn down, too far on that string (though I'd usually expect a buzz lower than the fifth fret) and that your truss rod doesn't need just a hair of loosening (this will affect all the strings, though, but it may be that one string is buzzing and the other five are JUST BARELY not).
