Abstract: Disclosed is a drill for drilling thin plates and which has a pair of major cutting edges each including an inner major cutting edge diagonally extending in an inner portion of the tip so as to form a protrusive leading part, and an outer major cutting edge radially extending in the tip, a chisel edge formed at the junction of the inner major cutting edges, and continuous flanks formed behind the inner major edges and the outer major cutting edges, respectively. The diameter of the leading part formed by the inner major cutting edges is in the range of 40 to 50% of the drill diameter, the point angle formed between the inner major cutting edges is in the range of 100.degree. to 115.degree., the outer corner angle formed between the outer major cutting edge and a plane perpendicular to the axis of the drill is in the range of 4.degree. to 10.degree., and no margin is formed in the circumference of the tip.

Abstract: A twist drill including a body characterized by the outer portion of each of the heels bulging toward the main flute as compared with that of the standard twist drill, the main lips each bulging in a triangular shape in cross section toward the main flute as compared with that of the standard twist drill, and a subflute having a substantially U-shaped cross section and axially formed in the inner portion adjacent to the axis of the twist drill of each of the heels along the main flute for a predetermined distance from the tip.