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

A cutting insert, comprising:

• an upper surface;
• a lower surface located on a side opposite to the upper surface;
• a front lateral surface located between the upper surface and the lower surface;
• and
• a rear lateral surface located between the upper surface and the lower surface and located on a side opposite to the front lateral surface,
• the upper surface comprising
• a first upper cutting edge located on an intersection with the front lateral surface, and
• an upper constraining surface which is located closer to the rear lateral surface than the first upper cutting edge, and which is contactable with a holder,
• the lower surface comprising a lower constraining surface contactable with the holder,
• the lower constraining surface comprising a lower protrusion extended from a side of the front lateral surface toward the rear lateral surface,
• the lower protrusion comprising
• a first region located on a side opposite to the upper constraining surface,
• a second region located closer to the front lateral surface than the first region, and
• a third region located closer to the rear lateral surface than the first region, wherein
• a wedge angle of the first region is a first angle, a wedge angle of the second region is a second angle and a wedge angle of the third region is a third angle in a cross section orthogonal to an extending direction of the lower protrusion, and
• the first angle is smaller than each of the second angle and the third angle.