Abstract: A rotary air percussion drill bit which has a cylindrical body portion with first and second ends. A flat bottom face comprises one end with a shaft attached to the remaining end. A plurality of hard inserts is mounted in the body portion and projects downwardly from both the body portion and from the flat bottom face. The rotary air percussion drill bit has a first chip clearance means formed into the body portion longitudinally along its side wall with a second chip clearance formed around the side wall intermediate the first and second ends. The improvement in the rotary air percussion drill bit provides for a vertical slot which cuts through the drill base down the drill body and forms an arcuate terminus tapered to the cylindrical wall to the drill bit. A gauge tooth is mounted in the arcuate terminus at approximately 20.degree. to 35.degree. with a line normal to the axis of the drill bit.