PURPOSE: To prolong the service life of a metal blade and to reduce the necessary volume of the blade by shrink fitting the face parallel to the axis of the stairway of the base metal having a step like inner periphery in the axial direction to the face parallel to the axis of the stairway of the annular metal blade having a step like outer periphery in the axial direction.

CONSTITUTION: A blade is composed of a base metal 2 to which a face 3 having the step like outer peripheral face of a metal blade 1 and parallel to the axis of the step thereof and a face 4 having a step like inner periphery in the axial direction and parallel to the axis of the step thereof are press-fitted by shrink fitting. A compressive stress is generated in the circumferential direction of the blade tip part of the blade 1, the size thereof is reduced toward the center, the stress in the circumferential direction of the tooth tip part of the blade 1 generated at shearing time and the stress distribution by the shrink fitting are composed and the tensile stress at the tooth tip part of the blade 1 is reduced. The life of the blade 1 is therefore prolonged drastically, the necessary volume is reduced with its simple structure because of a tapered part being not provided in the shape thereof and the manufacture is simplified as well.