A roller cone drill bit is disclosed which includes a bit body adapted to be coupled to a drill string. A bearing journal depends from the bit body. A single roller cone is rotatably attached to the bearing journal. The roller cone has a plurality of inserts disposed at selected positions about the cone. The journal defines a rotation angle with respect to an axis of rotation of the bit such that the roller cone includes a wall contact zone and a bottom contact zone. At least one of the inserts disposed in the wall contact zone has an extension portion terminating in a substantially planar upper surface.