Cutting insert for indexable drill

A cutting insert for an indexable drill, comprising:

• opposing front and rear reference surfaces and a peripheral surface extending therebetween, the peripheral surface comprising opposing internal side surfaces and opposing external side surfaces, a fastening hole penetrating the front reference surface and the rear reference surface;
• in a top plan view of the front reference surface, the internal side surfaces have a first width (w1) and the external side surfaces have a second width (w2), wherein the first width (w1) and the second width (w2) are different from each other;
• each external side surface includes a first external side surface, a second external side surface and an external point surface located in-between the first and second external side surfaces, the external point surface is also located at a center of each respective external side surface;
• a front external cutting edge at an intersection of the front reference surface and each of the external side surfaces, a rear external cutting edge at an intersection of the rear reference surface and each of the external side surfaces,
• each of the front and rear external cutting edges includes a first external cutting edge, a second external cutting edge, an external point edge formed at the center of each respective external side surface, and an external transition cutting edge located in-between the first and second internal cutting edges;
• a front internal cutting edge at an intersection of the front reference surface and each of the internal side surfaces, a rear internal cutting edge at an intersection of the rear reference surface and each of the internal side surfaces,
• each of the front and rear internal cutting edges includes a first internal cutting edge, a second internal cutting edge, and an internal transition cutting edge located in-between the first and second internal cutting edges;
• in the top plan view of the front reference surface, a first angle (a1) is formed between the first internal cutting edge of a respective internal cutting edge and the first external cutting edge of a respective external cutting edge, a second angle (a2) is formed between the second internal cutting edge of the opposite internal cutting edge and the second external cutting edge of the respective external cutting, the first angle (a1) and the second angle (a2) are equal;
• wherein the cutting insert has 180° rotational symmetry about a longitudinal center axis of the fastening hole;
• wherein the cutting insert has 180° rotational symmetry around an axis connecting centers of the internal side surfaces, and the cutting insert has 180° rotational symmetry around an axis connecting the centers of the external side surfaces;
• and
• wherein each first internal cutting edge has a flat land that forms a right angle with respect to a corresponding internal side surface and a negative land that forms a first obtuse angle with respect to the corresponding internal side surface, the negative land is formed in partial sections of the first internal cutting edge.