In one aspect of the invention, a roller assembly has an axle that supports opposing faces of a cylindrical body that has a plurality of pointed inserts disposed along an outer diameter of the cylindrical body. At least one of the inserts has a tip with a polycrystalline diamond bonded to a cemented metal carbide segment. The diamond has a substantially conical geometry with a 0.50 to 0.200 inch radius apex and comprises a thickness greater than 0.100 inches at the apex. The roller assembly has an internal lubrication mechanism adapted to apply lubrication between the axle and the cylindrical body.