Patent attributes
Multiple grooves are provided on the outer circumferential surface of the body of an insert holder. A first holding surface of an insert first holding part, which is inserted between a groove bottom and a first protrusion, and a first protrusion surface of the first protrusion make surface contact and said surfaces are sloped so as to approach the groove bottom as the first end is approached. A second holding surface of an insert second holding part, which is inserted between the groove bottom and a second protrusion, and a second protrusion surface of the second protrusion make surface contact and said surface are sloped so as to approach the groove bottom as the second end is approached.