A drill body for a drill having a rotational axis, comprising: an inner pocket formed adjacent to the rotational axis at a proximal end of the drill body; and an outer pocket formed further away from the rotational axis than the inner pocket at the proximal end of the drill body, wherein each of the pockets comprises a first wall (51, 61, 51"", 61"") facing the workpiece, a second wall (51', 61', 51"', 61'") substantially perpendicular to the first wall and disposed adjacent to the rotational axis of the drill body, and a bottom surface (71, 71'); the first walls of the inner and outer pockets include identical surface shapes while the second walls of the inner and outer pockets include identical surface shapes; characterized in that: each of the first wall and the second wall comprise a respective flat lower side surface (61, 61', 61'", 61"") adjacent to the bottom surface and a respective curved upper surface (51, 51', 51'", 51 "") extending from the lower side surface; and wherein each of the upper side surface of the first wall of the inner pocket and the upper side surface of the first wall of the outer pocket comprises a first part surface (82, 82""), a transition part surface (84, 84"") and a second part surface (86, 86"") sequentially arranged in a direction away from the rotational axis, and wherein the first part surface of the upper side surface of the first wall of the inner pocket and the second part surface of the upper side surface of the first wall of the outer pocket incline toward the rotational axis of the drill body in a direction toward the workpiece; and/or wherein each of the upper side surface of the second wall of the inner pocket and the upper side surface of the second wall of the outer pocket comprises a first part surface (82', 82"'), a transition part surface (84', 84"') and a second part surface (86', 86"') sequentially arranged in a direction away from the workpiece, and wherein the first part surface of the upper side surface of the second wall of the inner pocket inclines toward the workpiece in a direction toward the rotational axis of the drill body while the second part surface of the upper side surface of the second wall of the outer pocket inclines toward the workpiece in a direction away from the rotational axis of the drill body. an inner pocket formed adjacent to the rotational axis at a proximal end of the drill body; and an outer pocket formed further away from the rotational axis than the inner pocket at the proximal end of the drill body, wherein each of the pockets comprises a first wall (51, 61, 51"", 61"") facing the workpiece, a second wall (51', 61', 51"', 61'") substantially perpendicular to the first wall and disposed adjacent to the rotational axis of the drill body, and a bottom surface (71, 71'); the first walls of the inner and outer pockets include identical surface shapes while the second walls of the inner and outer pockets include identical surface shapes; characterized in that: each of the first wall and the second wall comprise a respective flat lower side surface (61, 61', 61'", 61"") adjacent to the bottom surface and a respective curved upper surface (51, 51', 51'", 51 "") extending from the lower side surface; and wherein each of the upper side surface of the first wall of the inner pocket and the upper side surface of the first wall of the outer pocket comprises a first part surface (82, 82""), a transition part surface (84, 84"") and a second part surface (86, 86"") sequentially arranged in a direction away from the rotational axis, and wherein the first part surface of the upper side surface of the first wall of the inner pocket and the second part surface of the upper side surface of the first wall of the outer pocket incline toward the rotational axis of the drill body in a direction toward the workpiece; and/or wherein each of the upper side surface of the second wall of the inner pocket and the upper side surface of the second wall of the outer pocket comprises a first part surface (82', 82"'), a transition part surface (84', 84"') and a second part surface (86', 86"') sequentially arranged in a direction away from the workpiece, and wherein the first part surface of the upper side surface of the second wall of the inner pocket inclines toward the workpiece in a direction toward the rotational axis of the drill body while the second part surface of the upper side surface of the second wall of the outer pocket inclines toward the workpiece in a direction away from the rotational axis of the drill body.