Cutting insert, cutting tool, and method for manufacturing machined product

A cutting insert comprising

• a body having a flat plate shape and comprising:
• a first main surface having a polygonal shape;
• a second main surface located opposite to the first main surface;
• an outer peripheral surface located between the first main surface and the second main surface;
• a through-hole penetrating the first main surface and the second main surface;
• a main body portion which is a region of the body including the through-hole and surrounding of the through-hole;
• and
• corner portions which is a region other than the main body portion, at least one of the corner portions being a cutting portion,
• wherein the main body portion has a thickness larger than a thickness of the cutting portion,
• a protruding portion is provided in a main body portion outer peripheral surface of the main body portion, and
• the protruding portion comprises a curved outer surface in a front view of the first main surface.

A cutting insert having a flat shape, and comprising:

• a first surface comprising:
• a first center region that comprises:
• a first opening;
• and
• a first side that comprises a first curved side;
• and
• a first corner region next of the first center region, comprising second and third sides;
• a second surface opposed to the first surface:
• a second center region opposed to the first center region, and comprising:
• a second opening;
• and
• a fourth side that is opposed to the first side and comprises a second curved side that is opposed to the first curved surface;
• a second corner region next of the second center region, opposed to the first corner region, and comprising fifth and sixth sides opposite to the second and third sides respectively;
• a side surface between the first surface and the second surface, connecting the first, second and third sides with the fourth, fifth and sixth sides, respectively, and comprising a curved side surface that connects the first curved side with the second curved side;
• and
• a through-hole connected the first opening and the second opening;
• wherein a first distance between the first center region and the second center region is larger than a second distance between the first corner region and the second corner region.