a device for boring holes; it is in the form of a cylindrical spindle with radially placed holes, either rectangular or round, in which individual or block cutters are fastened. Boring bars usually have a shaft that is fastened to the spindle of a boring machine. If the bar is long, the opposite end is held and guided by a sleeve on an end support. If the workpiece is fastened to a fixture rather than to the machine itself, the boring bar is directed by jig bushings, and the connection of the boring bar to the spindle is made with a coupling permitting self-alignment of boring-bar axis.

Various boring bars are designed to permit radial feed of the cutters for adjustment—that is, for compensation of the dimensional wear of the cutters—or the machining of indentations and grooves. Boring bars may be equipped with vibration dampers to reduce the level of vibrations arising in the cutting process.