Abstract: A sealed rotary drill bit comprising at least one rotatably carried roller cutter (13) and provided with a seal between the cutter and a mounting head (22) for preventing lubricating medium from being discharged from the bearing (14, 15, 16, 17, 18) and impurities from entering the bearing. For purposes of decreasing the friction the seal (22) is provided with a low friction material on a portion of the seal which engages the head to promote rotation between the seal and the head. The portion of the seal which engages the roller cutter has a material of higher frictional coefficient to resist relative rotation between the seal and the roller cutter (25).

Abstract: A rotary drill bit comprising a roller cutter (12) which is rotatably carried over a bearing system. The bearing system comprises at least one roller bearing (16). Fluid is supplied to the bearing system for flushing and lubricating and when needed cooling thereof. For purposes of ensuring suitable fluid flow through the roller bearing (16) and thus ensuring satisfactory lubrication thereof the rollers in the roller bearing (16) are provided with an axial bore (25).