Kelly and kelly drive bushing

摘要

An improved kelly is provided with a drive section which has a uniform cross section defined by three generally flat drive sides alternating with three generally arcuate sides. The three arcuate sides are spaced an equal radii from the central axis of the kelly and the three flat drive sides lie in planes that form an equilateral triangle therebetween. The improved kelly is driven by an improved mating kelly drive bushing which has three rollers positioned so as to evenly transmit torque to the three flat drive sides of the kelly simultaneously.