A drive shaft assembly comprising: (a) a drive shaft having a first end, a second end, and a longitudinal rotational axis (A-20), said first end being formed with an integral, convexly spherical bearing surface; (b) a first end housing having a longitudinal rotational axis (A-40), and having a concavely spherical bearing surface, wherein the concavely spherical bearing surface mates and slidably engages the convexly spherical bearing surface of the first end of the drive shaft; and (c) means for transferring torque from the drive shaft to the first end housing when the convex bearing surface of the first end of the drive shaft is in mating engagement with the concave bearing surface of the first end housing, said means for transferring torque being operationally effective irrespective of any relative angular offset between the rotational axes (A-20, A-40) of the drive shaft and the first end housing, within a selected angular range; wherein: (d) the means for transferring torque comprises a pair of first drive keys, each of the first drive keys having a drive key head, wherein the first drive keys are mounted to the drive shaft on opposite sides thereof and are swivellable about a first swivel axis (A-60) perpendicular to and passing through the rotational axis (A-20) of the drive shaft; (e) each first drive key head has a planar end face; (f) the first end housing has a pair of first drive key slots, each of the first drive key slots having a side face oriented parallel to the rotational axis (A-40) of the first end housing; and (g) each first drive key head is disposed within one of the first drive key slots, such that rotation of the drive shaft in a first rotational direction will urge the end face of each first drive key head into force-transferring contact against the side face of the corresponding first drive key slot, with each first drive key head being slidable within its corresponding first drive key slot to accommodate angular variances between the rotational axes (A-20, A-40) of the drive shaft and the first end housing; characterized in that: the convexly spherical bearing surface extends radially inward on the first end to the longitudinal rotational axis (A-20) of the drive shaft, and the concavely spherical bearing surface extends radially inward to the longitudinal rotational axis (A-40) of the first end housing. (a) a drive shaft having a first end, a second end, and a longitudinal rotational axis (A-20), said first end being formed with an integral, convexly spherical bearing surface; (b) a first end housing having a longitudinal rotational axis (A-40), and having a concavely spherical bearing surface, wherein the concavely spherical bearing surface mates and slidably engages the convexly spherical bearing surface of the first end of the drive shaft; and (c) means for transferring torque from the drive shaft to the first end housing when the convex bearing surface of the first end of the drive shaft is in mating engagement with the concave bearing surface of the first end housing, said means for transferring torque being operationally effective irrespective of any relative angular offset between the rotational axes (A-20, A-40) of the drive shaft and the first end housing, within a selected angular range; (d) the means for transferring torque comprises a pair of first drive keys, each of the first drive keys having a drive key head, wherein the first drive keys are mounted to the drive shaft on opposite sides thereof and are swivellable about a first swivel axis (A-60) perpendicular to and passing through the rotational axis (A-20) of the drive shaft; (e) each first drive key head has a planar end face; (f) the first end housing has a pair of first drive key slots, each of the first drive key slots having a side face oriented parallel to the rotational axis (A-40) of the first end housing; and (g) each first drive key head is disposed within one of the first drive key slots, such that rotation of the drive shaft in a first rotational direction will urge the end face of each first drive key head into force-transferring contact against the side face of the corresponding first drive key slot, with each first drive key head being slidable within its corresponding first drive key slot to accommodate angular variances between the rotational axes (A-20, A-40) of the drive shaft and the first end housing; the convexly spherical bearing surface extends radially inward on the first end to the longitudinal rotational axis (A-20) of the drive shaft, and the concavely spherical bearing surface extends radially inward to the longitudinal rotational axis (A-40) of the first end housing.