Patent ID: 6991267

Claim:
An elongated drive string assembly comprising a plurality of hollow sucker rods and connecting elements with an axis, connected together and between a drive head located at the surface of an oil well and a rotary pump located deep down the oil well, wherein at least one hollow sucker rod has a first end comprising an internal female threaded surface engaging an external male threaded surface on at least one connecting element, wherein said threads are frusto-conical and non-symmetrical, but differential in diametral taper to each other; the first end of said at least one hollow sucker rod further comprising an annular torque shoulder that is engaging an annular torque shoulder on said at least one connecting element and being characterized in that, for an outside diameter of the connecting element (DEN), an internal diameter (DIN) of the connecting element, and a starting diameter of the torque shoulder on the connecting element (DHT), the following ratios are maintained: Range Diameter Ratios Min. Max. DHT/DEN 0.60 0.98 DIN/DEN 0.15 0.90 DIN/DHT 0.25 0.92 wherein said at least one connector element is a separate nipple having said male threaded surface on at least one free end of that nipple and a central section defining said engaging torque shoulder, and said male threaded surface of said nipple free end comprising complete threads, said nipple free end further comprises a portion that is adapted to engage against an inner surface of the rod, so as to define a seal between an inner bore of the hollow rod and the complete threads.