Or a screw, a pencil and a length of wire or string. The cutout for most 6.5s is 5.75" and the outside diameter will be ~6.625-6.75.
Put the screw in the center of the workpiece, attach one end of the wire or string to it and then measure from the screw to half the diameter of the circles you want to make. Then wrap the wire (a sold piece works best) or string around the pencil and trace the circles.