A downhole drilling apparatus , comprising: a first member comprising an outer surface connector extending from a second end of the first member , a groove in a first end of the first member and a hole penetrated by a longitudinal axis of the first member ; a second member comprising an outer surface connector extending from a second end of the second member , a tongue in a first end of the second member and a hole penetrated by a longitudinal axis of the second member ; a plurality of intermediary members positioned between the first and second members, each intermediary member comprising a groove in a first end and a tongue in a second end of the intermediary members , wherein each intermediary member includes a hole penetrated by a longitudinal axis of each intermediary member , and wherein the groove in the first end and the tongue in the second end of each intermediary member are oriented out of alignment with each other, wherein the first member , the plurality of intermediate members , and second member are connected in series by engaging the tongues and grooves of adjacent members to transfer torque therethrough, a coupling element to mechanically couple the first and the second members , wherein the coupling element traverses the holes penetrated by the longitudinal axes of the first member , the second member , and the intermediary members , to apply a compressive force between the first and second members , wherein the apparatus further comprises a drive shaft for turning a drill head rotatable about a rotation axis and a rotor rotatable in a circular path about the axis, wherein the outer surface connector of either the first or the second member couples to the drive shaft for rotation therewith and the outer surface connector of the other of the first or the second member couples to the rotor for rotation therewith. a first member comprising an outer surface connector extending from a second end of the first member , a groove in a first end of the first member and a hole penetrated by a longitudinal axis of the first member ; a second member comprising an outer surface connector extending from a second end of the second member , a tongue in a first end of the second member and a hole penetrated by a longitudinal axis of the second member ; a plurality of intermediary members positioned between the first and second members, each intermediary member comprising a groove in a first end and a tongue in a second end of the intermediary members , wherein each intermediary member includes a hole penetrated by a longitudinal axis of each intermediary member , and wherein the groove in the first end and the tongue in the second end of each intermediary member are oriented out of alignment with each other, wherein the first member , the plurality of intermediate members , and second member are connected in series by engaging the tongues and grooves of adjacent members to transfer torque therethrough, a coupling element to mechanically couple the first and the second members , wherein the coupling element traverses the holes penetrated by the longitudinal axes of the first member , the second member , and the intermediary members , to apply a compressive force between the first and second members , wherein the apparatus further comprises a drive shaft for turning a drill head rotatable about a rotation axis and a rotor rotatable in a circular path about the axis, wherein the outer surface connector of either the first or the second member couples to the drive shaft for rotation therewith and the outer surface connector of the other of the first or the second member couples to the rotor for rotation therewith. <EOS>