Insert type tool and thread mill

An insert type tool comprising:

• a cylindrical body that extends in an axial direction;
• a disc-shaped insert portion;
• and
• a fixing device that detachably fixes the insert portion to one end portion in the axial direction of the body, wherein
• the insert portion can be configured by a single disc-shaped insert or by a plurality of the inserts coaxially overlaid with each other, an outer periphery of the insert including blade portions for machining and the insert having two faces that are arranged parallel in a thickness direction thereof, one of the faces being a front face at a front side of the insert and the other of the faces being a back face at a back side of the insert,
• the insert, on the front face and the back face, comprises:
• convex portions respectively protruding from a center in the thickness direction of the insert to both of the front and back sides in the thickness direction, the convex portions being most separated from the center;
• and
• concave portions provided in sections excluding the convex portions, the concave portions respectively protruding from the center to the both of the front and back sides in the thickness direction, and the concave portions being lower than the convex portions such that a thickness of the concave portions, which is determined in the thickness direction, is smaller than a thickness of the convex portions, and
• when the plurality of the inserts are coaxially overlaid with each other wherein one of the inserts mates with another of the inserts at a mating face, on each of the mating faces of all the inserts that are overlaid with each other, convex portions provided on a mating face of a first insert are inserted in concave portions provided in a mating face of a second insert, and the convex portions provided on the mating face of the second insert are inserted in the concave portions provided in the mating face of the first insert, the first insert being one insert of adjacent two of the inserts, and the second insert being another insert of the adjacent two of the inserts, and
• the blade portions are disposed at only outer peripheries of the convex portions such that no blade portion is disposed at outer peripheries of the concave portions.