Abstract: A boring bar holder for use with a lathe has a massive metal block with a generally triangular cavity extending transversely across the block. Inside the cavity a pair of diagonally extending surfaces are defined by the inside of upper and lower walls which intersect one another along a centering line. A U-shaped clamp rides in longitudinal grooves on sides of the block providing legs that have contact surfaces on ends of the legs. When the U-shaped member is forced forward, ends of the legs and the upper and lower wall grip the boring bar from three sides, causing the bar to be forced into position parallel to a centering line. A wide size range of boring bars can be held by this device with minimal adjustment, and change-out of bars is readily carried out when needed.