Are you talking the heavy cable that carries the power to crank the starter? The one that goes on the big stud, or the small wires that come off with plug in connectors?
If you mean the small wires 16 ga is ok.
On the big studs, stock is like 10 or 8 ga. I use 6 ga. I also run an extra ground from one of the starter bolts straight to the battery negative.
Leo