Drilling tool

In a drilling tool, particularly for working metals, including a tool holder having a receiving slot which is open on three sides formed in its end surface, an interchangeable blade type drill bit inserted in said slot, and means for fastening said drill bit in said slot, the improvement comprising a bar-shaped adapter symmetrically disposed in said receiving slot between said drill bit and the bottom surface of said receiving slot, said adapter extending laterally beyond the periphery of said tool holder for a distance equal to or slightly less than the lateral expanse of said drill bit, said adpater having a first end surface which abuts said bottom surface of said receiving slot and a second opposite end surface which contacts and provides an abutment for at least the portions of the adjacent end surface of said blade shaped drill bit which extend beyond the periphery of said tool holder, said adjacent end surface of said drill bit being opposite the end surface thereof containing the cutting tip of the drill bit;

• a recess formed in the center of said second end surface of said adapter;
• and a mating protrusion formed on said adjacent end surface of said drill bit for centering said drill bit.