Tapered pipe thread-machining spiral tap

A spiral tap that is to be rotated about a rotation axis for machining a pipe tapered thread, said spiral tap comprising a tapered thread portion having a thread profile that 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 at least one of said lands having a cutting edge that is defined by one of opposite ends of said each of said at least one 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 flutes consist of a plurality of spiral flutes that are three, four or five spiral flutes each having a helix angle that is not smaller than 30° and smaller than 50°, and
• a flute width ratio AG/(AG+AL) is 0.3-0.5, where AG represents a central angle which is subtended by each of said flutes and which is defined at a center corresponding to said rotation axis in a cross section that is perpendicular to said rotation axis, and AL represents a central angle which is subtended by each of said lands and which is defined at said center in said cross section.