Thread forming tap and manufacturing method for thread forming tap

A thread forming tap comprising a complete thread portion including threads, and a chamfer portion continuously formed with the complete thread portion and including a tapered thread, a part of the thread at a front end of the chamfer portion being configured as an incomplete thread portion including an incomplete thread, and the thread forming tap forming internal threads by means of plastic deformation, wherein

• the incomplete thread portion has lobes protruding in radial directions as viewed in a direction of the axis of the complete thread portion, reliefs having diameters smaller than those of the lobes, and an inclined bevel surface formed on a front end side of the chamfer portion by beveling the incomplete thread,
• the tapered thread in the chamfer portion continuously formed with the incomplete thread portion includes a bevel portion having the inclined bevel surface formed by beveling a flank of the tapered thread in the chamfer portion, the flank being located on the front end side of the chamfer portion,
• the thread in the incomplete thread portion and the bevel portion is formed such that the height of the thread gradually increases along a helix of the thread from the front end of the chamfer portion,
• a part of the thread closest to the front end of the chamfer portion includes a plurality of the inclined bevel surfaces formed by beveling the incomplete thread,
• each of the plurality of the inclined bevel surfaces is formed as a planar surface that is inclined so as to be positioned closer to the complete thread portion toward a crest of the thread, and
• the plurality of the inclined bevel surfaces are sequentially arranged around the axis, and a tip of a respective one of the lobes is located at a boundary between neighboring ones of the inclined bevel surfaces arranged around the axis.