<p>A boring bar has a body formed with an axial cut at the portion near its tip to define a pair of cut-apart portions. Insert mounting portions are provided on mutually opposite ends of the cut-apart portions at a tip end of the cut. A dimension adjusting mechanism is provided at an intermediate portion of the cut-apart portions. A dimension adjusting mechanism is provided at an intermediate portion of the cut-apart portions to change a boring diameter between the tips of cutting edges of inserts mounted on the insert mounting portions by moving the cut-apart portions along surfaces of the cut. A fixing screw is provided between a tip of the cut-apart portions and the dimension adjusting mechanism to fix the cut-apart portions together after adjusting the dimensions. In another arrangement, another cut is formed in the bar body at its end opposite from the end on which the inserts are mounted. A covering member is mounted on the bar body to cover this cut. It carries adjusting screws on both sides of the cut to press the bar body in a diametric direction. <IMAGE></p>
