Abstract: A cutting tap comprises a threaded portion including a lead whose thread diameter gradually decreases toward a front end of the lead, a complete thread portion continued from the lead, and four flutes arranged at equal intervals in a circumferential direction. In the cutting tap, a first cutting edge portion for processing a prepared hole is formed at a front end surface of the lead, and a second cutting edge portion for finishing a minor diameter of an internal thread is formed in a part of an outer periphery of the complete thread portion, the second cutting edge portion being one or more pitches long. The cutting tap can perform processing of a prepared hole, tapping, and finishing of a minor diameter by a single step, and can also perform tapping even if a prepared hole for an internal thread is a blind hole or the like and does not have enough space.

Abstract: A tap having a reamer edge which is provided at a chamfer part, so that when the thread forming tap is pulled out after the internal thread is formed, a seam portion present at the crest of the internal thread is cut off, whereby even in a blind hole, formation of internal thread and cutting of the seam portion are performed in a single process, and formation of an internal thread and processing of an inside diameter portion are achieved in a single process to obtain concentricity in line with each other. Further, even if there is a deviation in diameter of the hole before threading, the inside of the internal thread is processed to a constant value.

Abstract: In a tap having a lead part and a complete thread part contiguous to the lead part, a relief is formed on at least one of a leading flank and a following flank of each of a plurality of thread ridges formed on the rear end side of the lead part and each of a plurality of thread ridges formed on the front end side of the contiguous complete thread part, so that the portion of an internal thread having been cut already by the preceding cutting edge may not be cut again and widened by the succeeding cutting edge.