An insert rotary cutter inludes a cutter body (10) having a forward end face (16) and at least one first cutter insert (12) releasably attached to the cutter body (10). The first cutter insert (12) is of a generally triangular shape including a front face (30) having three marginal ridges and three corner ridges. Each marginal ridge is comprised of first, second and third ridge portions. The insert has three main cutting edges (36) each defined by a respective first ridge portion, three auxiliary cutting edges each defined by a respective third ridge portion, three corner cutting edges each defined by a respective corner ridge, and three relief cutting edges each defined by a respective second ridge portion. One of the corner cutting edges and the main (36) and auxiliary cutting edges which intersect the corner cutting edge are indexed in active cutting position. The indexed main cutting edge (36) extends generally axially from the body (10) while the indexed auxiliary cutting edge extends slightly beyond the forward end face (16). The relief cutting edge which intersects the indexed auxiliary cutting edge being displaced rearwardly from the indexed auxiliary cutting edge.
