Abstract: A diameter adjustment oriented balancing system is disclosed for use with small diameter rotary boring heads. The diameter adjustment oriented balancing system includes a rotary boring head with a radially movable tool carrier. The rotary boring head designed to receive a number of removable counterweights in one or more slots precisely aligned in the axis of radial movement of the tool carrier. The diameter adjustment oriented balancing system further comprises a series of boring bars which are designed to be perfectly balanced such that the combination of the rotary boring head and cutting tool holder is perfectly balanced when the center of the cutting tool holder is located at the center of the rotational axis of the rotary boring head.