retained on the bit face while exposing a maximum extent of the polycrystalline diamond element sandwiched between the prepad and trailing support application_number US 47516883 A description synthetic polycrystalline diamonds are readily available at a cost highly competitive with similarly sized natural diamonds of industrial quality and have virtually the same if not better wear characteristics and generally less friability in addition synthetic diamonds have the particular advantage of being manufactured in uniform and regular shapes which can be exploited to maximize cutting efficiency however thermally stable polycrystalline diamond pcd elements are manufactured in such sizes that their retention on the face of a drill bit is not a trivial matter pcd elements currently manufactured by general electric company under the trademark geoset are triangular prisms having an equilateral triangular cross section perpendicular to the longitudinal axis of the triangular prismatic shape the typical dimensions of such pcds presently available are 2 6 millimeters in length and 4 0 millimeters on a side a larger sized thermally stable geoset 6 0 mm on a side and a 3 7 mm thick are also now available according to the present invention such pcd elements can be retained upon the face of a rotary bit provided that the projecting portion of each pcd is supported by integral matrix material extending from the rotary bit face to form a prepad and tail support the prepad and tail support have a mutually congruent triangular cross section and together.