An indexable triangular-shaped cutting insert comprising: opposing upper and lower end surfaces (22, 24) with a peripheral surface extending therebetween and a central axis extending therethrough, the peripheral surface including three side surfaces circumferentially alternating with three corner surfaces, each corner surface intersecting the upper end surface to form an upper cutting edge, and each side surface having an inwardly recessed locating surface, the lower end surface having a raised lower support surface and three lower abutment recesses circumferentially spaced around the lower support surface, each lower abutment recess including a radially outward facing lower abutment surface, wherein: in a first cross-section taken in a median plane perpendicular to the central axis and intersecting the three locating surfaces, the three locating surfaces define a first imaginary triangle having: three first sides and three first corners, three first bisector planes (P B 1), each first bisector plane (P B 1) containing the central axis and bisecting one of the three first corners, and three vertical locating planes (P VL), each vertical locating plane (P VL) being perpendicular to the median plane and containing one of the three first sides, in a second cross-section taken in a horizontal lower plane (P HL) parallel to the median plane and intersecting the three lower abutment surfaces, the three lower abutment surfaces define a second imaginary triangle having: three second sides and three second corners, and three second bisector planes (P B 2), none of the three second bisector planes (P B 2) is coplanar with any of the three first bisector planes (P B 1), characterized in that each second bisector plane (P B 2) is containing the central axis and is bisecting one of the three second corners, and each vertical locating plane (P VL) intersects two of the upper cutting edges. the peripheral surface including three side surfaces circumferentially alternating with three corner surfaces, each corner surface intersecting the upper end surface to form an upper cutting edge, and each side surface having an inwardly recessed locating surface, the lower end surface having a raised lower support surface and three lower abutment recesses circumferentially spaced around the lower support surface, each lower abutment recess including a radially outward facing lower abutment surface, in a first cross-section taken in a median plane perpendicular to the central axis and intersecting the three locating surfaces, the three locating surfaces define a first imaginary triangle having: three first sides and three first corners, three first bisector planes (P B 1), each first bisector plane (P B 1) containing the central axis and bisecting one of the three first corners, and three vertical locating planes (P VL), each vertical locating plane (P VL) being perpendicular to the median plane and containing one of the three first sides, three first sides and three first corners, three first bisector planes (P B 1), each first bisector plane (P B 1) containing the central axis and bisecting one of the three first corners, and three vertical locating planes (P VL), each vertical locating plane (P VL) being perpendicular to the median plane and containing one of the three first sides, in a second cross-section taken in a horizontal lower plane (P HL) parallel to the median plane and intersecting the three lower abutment surfaces, the three lower abutment surfaces define a second imaginary triangle having: three second sides and three second corners, and three second bisector planes (P B 2), three second sides and three second corners, and three second bisector planes (P B 2), none of the three second bisector planes (P B 2) is coplanar with any of the three first bisector planes (P B 1), characterized in that each second bisector plane (P B 2) is containing the central axis and is bisecting one of the three second corners, and each vertical locating plane (P VL) intersects two of the upper cutting edges.