A hex, as in a bolt head?
I would start by drawing a circle with the diameter being the width of the flats you want. Then draw a straight line, then translate that line from the midpoint of the line to a quadrant on your circle. Then use the rotate and copy the line around the center of the circle, just input the number of flats that you want. Then just trim or extend your lines to create your intersection points.
I'm sure there are other ways to do it, but that's how I would tackle it first.