A drill structure includes a shank part and a flute part. A chisel edge is formed on the front end of the flute part and two primary relief faces with tile directions toward the shank part are symmetrically formed on the two sides of the chisel edge. Each primary relief face has a cutting edge, a knife-back edge, and an outer edge. The outer edges are respectively helically extended around the periphery of the flute part to form two helical cutting edges and two helical grooves. Two assist relief faces are respectively formed on the inner walls of the two helical grooves, and every assist relief face is connected with the cutting edge of one primary relief face and portion of the knife-back edge of another primary relief face. The drill structure can decrease the thickness of the chisel edge, reduces the resistance during drilling, and increases the life.

A drill bit including a body extending from a shank to a point angle, wherein the body includes a plurality of steps each associated with a different cutting diameter; a first groove disposed between a first pair of adjacent steps of the plurality of steps and radially inset from an outer diameter of each of the first pair of adjacent steps; and a first visual indicator disposed in the first groove.