US Patent 7186182 Drive line for down hole mud motor

A drive line for a down hole mud motor has a plurality of elongate keys extending radially from an exterior surface of a central shaft for the purpose of transmitting torque. A plurality of circumferentially spaced axial keyways are provided in an interior surface of each end housing, which are adapted to receive the keys. Each of the keys has opposed sides, opposed ends and a front face. The front face is radiused both in a first direction between the opposed ends and in a second direction between the opposed sides, thereby accommodating the omni-directional pivotal movement of the shaft relative to the housing. The use of keys for torque transmission increases available contact area, with a corresponding increase in torque load capacity.