Indexable thread forming tap

An indexable thread forming tap comprising:

• a body in a shaft shape;
• and
• a tip concentrically and detachably attached to a leading end portion of the body by screw-fastening and rotationally driven around an axial center along with the body for rolling of a female thread,
• the body being disposed with a screw hole concentrically to the axial center such that a screw shaft disposed on the tip concentrically to the axial center is screwed into the screw hole for the screw-fastening,
• a leading end surface of the screw shaft being pressed against a bottom surface of the screw hole into close contact with each other by the screw-fastening to integrally fix the tip to the body in a state where a predetermined gap is provided between a leading end of the body and the tip,
• the body being disposed with a restraining hole concentrically to the axial center such that a restraining portion disposed on the tip concentrically to the axial center is fitted into the restraining hole to position the body and the tip concentrically to the axial center,
• an outer diameter of the leading end surface of the screw shaft brought into close contact with the bottom surface of the screw hole being within a range of 30 to 55% of a machining diameter of the tip, and
• a nominal diameter of the screw hole and the screw shaft being within a range of 48 to 66% of a machining diameter of the tip.