Single-cone rock bit

A roller cone drill bit comprises a bit body 1 adapted to be coupled to a drill string, a bearing journal 1A depending from the bit body and a single roller cone 6 carrying inserts 5 rotatably attached to the bearing journal. The journal defines a rotation angle a between the axis of rotation 11 of the bit such that the roller cone includes an intermittent contact zone 20 and a continuous contact zone 22 thereon. The inserts 5 in the continuous contact zone 22 are made from a super hard material, such as diamond or boron nitride. The inserts may have an extension length of at least 0.6 inches (1.524 cm), may be arranged in columns such that one of the inserts is overlapped only by an adjacent one of the inserts in one of the columns, or may be arranged in helical columns, the columns being arranged so that a plane containing the axis of the cone intersects at least one and at most two of the columns on one side of the cone surface.