Abstract: A cutting tool assembly comprising a tool holder formed with an insert retaining pocket having a pocket base wall and in which is releasably mounted a cutting insert and a shim. The cutting insert is of a substantially prismatic shape having an upper surface, a lower surface and side relief flank surfaces and at least one cutting corner defined therebetween and presenting at least one cutting edge formed by the intersection of the upper surface and a corresponding number of the side relief surfaces adjacent thereto.