In one aspect, composite tool holders are described herein comprising advantageous structural arrangements of metal carbide and alloy components. Briefly, a composite tool holder comprises a metal carbide shank comprising a bore having an inner diameter and outer diameter. An alloy sleeve is positioned in the bore for engaging a tool, wherein the alloy sleeve is bonded to inner diameter surfaces of the bore via a crosslinked adhesive.

A screwing tool provided with a high-torsion handle including a screwing tool body and a screwing tool handle is provided. An inner hole in an irregular shape is formed in the screwing tool handle, and the shape of the top end of the screwing tool body is the same as that of the inner hole. The screwing tool body and the screwing tool handle are fixed to each other via high-strength glue, and the inner hole of the screwing tool handle is a semi-cylindrical inner hole, a triangular inner hole, a quadrilateral inner hole, a hexagonal inner hole, an octagonal inner hole or a decagonal inner hole. Since the inner hole of the handle is machined into the irregular polygon, all types of screwing tools including drill bits can be fixed to the screwing tool handle via the high-strength glue.

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.