An exchangeable cutting insert having a substantially prismatic shape is disclosed. The insert has an upper rake surface, an opposite, substantially parallel base surface and side surfaces, adjacent side surfaces intersecting at an insert corner. Each side surface also intersects with the rake surface so as to define a cutting edge. Each cutting edge comprises a major cutting edge portion extending from one insert corner and merging with a succeeding, associated minor cutting edge portion, which terminates in a successive insert corner. Chip diverting ribs respectively associated with each of the cutting edges are formed on the rake surface. Each rib extends from a region adjacent the merger of the major and minor cutting edge portions on its associated cutting edge, and is substantially coextensive with the region of merger and is spaced from this region by a portion of the rake surface.