Abstract: A drill bit for conical cutting elements, each secured to a bit segment by an annular locking bearing which is fed by a first lubrication system which directs high pressure lubricant through the bit segment and locking bearing to space external of the drill bit at lower atmospheric pressure; each cutting element is further coupled to the bit segment by a second annular bearing radially inward of the locking bearing and lubricated by a second lubrication system independent of the first; the second lubrication system defines a closed space containing lubricant and the second bearing with one boundary of this space being a flexible wall whose outside surface is exposed to the atmospheric pressure external of the drill, the wall being deflectable to equalize the pressure of the second lubrication system with the atmospheric pressure.

Abstract: A flexible coupling comprises first and second coupling halves, at least a part of the first being inserted into the other, and the two coupling halves being linked together for transmission of power by means of resilient elements, these elements being surrounded over most of their surface and precompressed by the coupling halves.