Boring tool and cutting insert

A cutting insert comprising:

• a base member;
• and
• a cutting member located on the base member, wherein
• wherein the base member includes
• a first side surface,
• a second side surface that is inclined with respect to the first side surface,
• a third side surface that is inclined with respect to each of the first side surface and the second side surface and that is contiguous to each of the first side surface and the second side surface, and
• a fourth side surface that is inclined with respect to each of the first side surface, the second side surface, and the third side surface, that is separated from each of the first side surface and the second side surface, and that is contiguous to the third side surface,
• when viewed in a direction perpendicular to the third side surface, a distance between the first side surface and the second side surface is decreased as further away from the fourth side surface, and
• an interface between the base member and the cutting member is provided along a plane parallel to the third side surface,
• wherein
• an arithmetic mean roughness of each of the first side surface, the second side surface, and the fourth side surface is more than or equal to 0.5 μm, and
• an arithmetic mean roughness of the third side surface is smaller than the arithmetic mean roughness of each of the first side surface, the second side surface, and the fourth side surface.