Taper thread-cutting spiral pipe tap

A spiral tap comprising a tapered thread portion having a helically extending thread whose profile becomes from an incomplete profile to a complete profile in a direction away from a distal end of a chamfered portion toward a complete thread portion, said tapered thread portion being circumferentially divided by flutes into a plurality of lands, each of said lands having a cutting edge that is defined by one of opposite ends of said each of said lands which is located on a front side of the other of said opposite ends in a direction of rotation of said spiral tap, such that said cutting edge extends along a corresponding one of said flutes, wherein

• said spiral tap is to be rotated about a rotation axis for machining a pipe tapered thread, such that the pipe tapered thread is cut by said chamfered portion and said complete thread portion of said spiral tap,
• said flutes are four spiral flutes by which said tapered thread portion is circumferentially divided into four lands as said plurality of lands, and said four lands have respective four cutting edges each corresponding to said cutting edge,
• said thread extending in a helical direction intersects with said four cutting edges, and said cutting edges includes a plurality of thread intersection portions at each of which a corresponding one of said four cutting edges intersects with said thread, each thread intersection portion of said plurality of thread intersection portions comprising a single intersection of said thread with said corresponding one of said four cutting edges,
• some of said thread intersection portions of said cutting edges are partially or entirely removed while the other of said thread intersection portions are not removed, such that at least one of each adjacent four of said thread intersection portions, which are adjacent in said helical direction and which are located in said complete thread portion, are removed, without at least another one of said each four of said thread intersection portion being removed,
• said thread intersection portions of said four cutting edges consist of four groups of said thread intersection portions, such that each of said four groups of said thread intersection portions consists of ones of said thread intersection portions that are portions of a corresponding one of said four cutting edges, and
• every two of said ones of said thread intersection portions of each of said four groups is removed, such that, in each of said four groups, at least one of said thread intersection portions that is removed and at least another one of said thread intersection portions that is not removed are alternately arranged in a direction in which a corresponding one of said four cutting edges extends.