Drilling tool systems including a drilling body and a drilling inserts are disclosed. The drilling inserts include four indexable cutting edges. The four cutting edges may each comprise a plurality of cutting edge segments. The plurality of cutting edge segments are provided at distinct angles with respect to a reference plane of the drilling insert to provide effective chip breaking and a stronger cutting edge at the drilling insert corners. Furthermore, the side surfaces of the drilling inserts allow the drilling insert to be more stably supported in a pocket of the drilling body. The drilling inserts may be used in a central pocket of a drilling body.

An insert according to an embodiment includes an upper surface including a corner part, a lower surface, a side surface, and a cutting edge. The cutting edge includes a first cutting edge located at the corner part, a second cutting edge adjacent to the first cutting edge, a third cutting edge adjacent to the second cutting edge, and a fourth cutting edge adjacent to the third cutting edge. Each of the third cutting edge and the fourth cutting edge has a concave curvilinear shape extending downward in a side view. A radius of curvature of the fourth cutting edge is smaller than a radius of curvature of the third cutting edge.

An indexable drill insert includes a drill body having a central longitudinal rotational axis (C.sub.L), the drill body comprising a shank portion and a fluted cutting portion, the fluted cutting portion having a front clearance face and a plurality of flutes, the fluted cutting portion includes a central insert pocket capable of receiving a central cutting insert and a peripheral insert pocket capable of receiving a peripheral cutting insert. For the central cutting insert, a central, longitudinal axis of a projection of the flute coolant exit aperture can intersect a vertical plane (PA1) having an area (A1) or a horizontal plane (PB1) having an area (A2). For the peripheral cutting insert, the central, longitudinal axis of the projection can intersect a vertical plane (PA2) having an area (A3) or a horizontal plane (PB2) having an area (A4).