I'm not sure how to accuratly measure a cable core, but if I stip the cover, twist the copper each core is about 1.5mm in diam which would make it around 15awg....

HT:M80,VP150,QS8,EP500 Outside:4xM3 Office:AudioBytes, Rumpus: M60,VP150,M22 Portable:2 x Airs