the 6 does not mean it is a 6 gauge wire.... that would be huge- like twice the size of your house wiring. It's just a number designation for sizing and nothing to do with the gauge size.

I just checked a few new plugs. The size of a #6 wire is 360 microns (.36mm= 27 gauge wire)- the #7 is just under 330 microns (.33mm= 28 gauge wire)- just about .0016" difference.

nice conversion chart- http://en.wikipedia.org/wiki/American_wire_gauge