Abstract: A coupled version of a threaded connection 10 includes first threads 16, 38 and second threads, 20, 34 on both elongate tubulars 14, 30 and a coupling 45. An integral joint version 50 preferably includes a first and second tapered threads 58, 60 on each of the connected tubular bodies 54, 56. The coupling preferably includes a dope entrapment cavity in one of the connected tubulars between the first and second threads. A tapered metal seal surface is provided preferably between the first and second threads. The second thread in a preferred embodiment is a hook thread with a negative rake angle. In another embodiment, the pin ends of a coupled connection may engage, with seals provided between the first and second threads on each tubular.

Abstract: A threaded pipe connection is shown which features a cylindrical metal-to-metal containment seal. In addition to the cylindrical sealing surfaces, the connection utilizes a separate ramp or ramp regions that simulate a pin swaging or a box expansion which results in the ability of the cylindrical components of the seal to assemble without interference or with only slight interference.

Abstract: The threading of a threaded tubular element includes at least one tangential multiple radius junction zone at the thread root, in particular on the load flank side. This zone include a principal arc with a radius where the support circle cuts the flank at a point. The tangent to this circle makes a strictly positive angle with the flank. The secondary arcs have lower radii that effect the tangential junction of the principal arc on one side to the flank and on the other side to the thread root. The radius of the principal are larger than that of the standard circle which passes through and which would alone constitute a tangential junction zone. Such a threaded element provides a threaded tubular connection which incorporates good resistance to both static and cyclic stresses.

Abstract: A thread form for a tubular connection of the type having a pin member adapted to be made-up with a box member to form a pipe joint as shown. The pin member has pin threads with thread crests and thread roots which are adapted to be made-up with a mating box member having a complimentary thread structure. The pin thread crests are formed between a stab flank and a load flank of the pin thread. The pin thread has a multi-facited complex profile stab flank for engaging a mating stab flank on the complimentary box member to provide a wedging interfit between the surfaces of the pin and box threads. The pin and box threads are also helically structured as a wedge.

Abstract: A submersible pump drop pipe and casing assembly and method of manufacture is disclosed. The drop pipe/casing has a seated connector and base. The seated connector has a first and second cylinder section, the first cylinder section being used to align and direct the base into the seated connector and to provide lateral strength to the pipe.

Abstract: The oilfield tubular pin and box connection includes double shoulders 16, 22. An inner sleeve 18 engages the box at shoulder 20, and provides one of the two shoulders 16, 22 for engaging the pin. The pin bore optionally may be provided with a similar sleeve 24, thereby providing one of the shoulders for engaging the box. The sleeve 18 may be secured to the box shortly after its manufacture, or may be added as a retrofit to an existing box with a single shoulder.

Abstract: A threaded joint to be expanded, including a lip at the end of the male element end a housing for the lip on the female element to make the threaded joint capable of being sealed and of having a maximum internal passage cross-section after being subjected to diametral expansion by more than 10%. The free male end surface is socketed before expansion into a partially transverse shoulder surface of the female housing through the matching rebating shapes of the surfaces. And, the male lip outer peripheral surface is arranged with little play of the internal peripheral surface of the female housing. Such a threaded joint is particularly useful for casings and tubings used in oil wells.

Abstract: A strengthened pipe fitting has an internally threaded surface and a compression band. The compression band is sized to compress the internally threaded surface sufficiently so that the pipe fitting is subjected to a compressive preload. The compression band is covered with a non-corrosive material.

Abstract: A pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis.

Abstract: A shoulder ring (10) for installing in the J-space between the installed pin ends within a coupling collar is taught having a body with a central opening therethrough, a first end face (12) on the body, an opposite end face (14) on the body, an inner surface (16) adjacent the central opening and extending between the first end face and the opposite end face and an outer surface (18) extending between the first end face and the opposite end face, the body having a substantially uniform cross sectional shape between the first end face, the opposite end face, the inner surface and the outer surface and the ring shaped such that its radius to the outer surface varies around the outer surface circumference to form a plurality of lobes (12).

Abstract: A flush-type integral threaded joint with truncated-cone threads, with two scaling surfaces 11′, 12′, 11″, 12″) set at the end of the threaded portions (7, 8), and with two annular scaling shoulders (5′, 6′, 5″, 6″). The two threaded portions (7, 8) of the male element (1) and female element (2), respectively, have the same value of conicity, and the two sealing surfaces (11′, 12′, 11″, 12″) are, in one case, conical or cylindrical, and in the other spherical. The threaded portion of each male and female element may have an end area with a thread that is not perfect.

Abstract: A seal for threaded joints of pipelines formed by pipes with outer threads joined by couplings with inner threads, the seal constituted by a substantially cylindrical sleeve of elastomeric material, wherein the outer surface of the sleeve has at least on part of its length a thread engaging the inner thread of the coupling. The sleeve can be enlarged at both ends by sealing lips. Preferably, the seal is used for joints of pipelines to convey fluids, especially corroding fluids, hydrocarbons and its derivates, and the like.

Abstract: A fitting for coupling a pump attachment to the inlet or discharge port of a pump or compressor has an annular body with an externally threaded nipple at one end and a circular flange at the other end. An axial aperture extends between the ends through openings at the nipple and the flange. The opening at the flange is internally threaded and begins at a recess in the flange. The threaded opening is of a standard ISO rated size complementary to the threaded nipple. A coupler kit is also disclosed having components to connect the device to the pump either in a mating flange connection using a hinge clamp or a threaded connection using a hose barb having a threaded end that threads into the opening in the fitting.

Abstract: Threaded joint for pipes consisting of a male member (1) and a female member (2), which are provided on the outer and inner surfaces respectively with two threading portions presenting a lead-in flank &bgr; such that 10°≦&bgr;≦25°, an abutment surface (9) being present at the end of said male member for abutment to a corresponding annular abutment surface (10) of the female member. The lead-in flanks of the male (1) and the female (2) members, upon make-up and with unloaded joint leave a gap (in the direction parallel to the axis (21) of the joint) varying from 0.01 to 0.12 mm. The internal and external diameters D3 and D4 (of the pipe portion not involved in the coupling with the female member) of said male member, the inner and outer diameters D1 and D2 of the abutment surface of the female member are linked by the relationship: (D22−D12)/(D42−D32)≧0.5.

Abstract: Threaded pipe joint comprising a male element (1) and a female element (2), threaded and provided with respective complementary sealing surfaces, which define, when screwed together, a notch (13) formed on the female element (2) of a predetermined length (X), and a space (7, 8) between the threads of predetermined section (S), forming reservoir to house the joint lubricant, which comes out of the volume between the threads of the female (2) and male (1) elements during the tightening of the joint.

Abstract: An expandable coupling arrangement for coupling first and second tubulars includes a male thread portion on an end of the first tubular and a female thread portion on an end of the second tubular. The thread portions comprise dovetail threads having flanks, roots and crests, wherein the flanks are inclined at an angle of greater than 10°.

Abstract: A guide tube for use in a rock drill string includes a main portion, a sleeve disposed at a first end of the main portion, and a male thread portion disposed at a second end of the main portion. The sleeve forms a recess having a female thread. A flush channel extends through the guide tube. The main portion includes a section of reduced cross-section disposed adjacent the sleeve for defining a generally radially extending shoulder between the waist and the sleeve. The shoulder serves to support the guide tube on a rig as percussion is applied to the guide tube for loosening a threaded joint between the guide tube and another member.

Abstract: A lower pull tube adapter has an enlarged body portion and an enlarged seal surface so that one size pull tube adapter may be used for a wide range of reciprocating downhole well pumps of different sizes and types.

Abstract: A threaded joint for an oil well pipe is provided which prevents the occurrence of galling at the time of repeated tightening and loosening and which provides a high degree of air tightness and has excellent galling resistance and air tightness without using a liquid lubricant such as a compound grease. 1. A lubricating film of an inorganic polymeric compound which has an M (metal element)—O (oxygen) backbone and has a solid lubricant dispersed therein is formed on a threaded portion or an unthreaded metal contact portion. 2. A phosphate film and the lubricating film of the inorganic polymeric compound is formed on the threaded portion or the unthreaded metal contact portion. 3. A Cu plating layer and the lubricating film of the inorganic polymeric compound or a lubricating film of a resin in which a solid lubricant is dispersed is formed on the threaded portion or the unthreaded metal contact portion. 4.

Abstract: Tool module interconnect for interconnecting to adjoining modules for insertion in a drill string features a system which permits making the electrical interconnection before assembly of the mechanical connections to interconnect the tool modules together. The interconnect comprises a hollow interconnect body open at both ends. A wire harness is provided in the hollow body with terminal end connectors accessible from the respective open end of the interconnect body. Both ends of the interconnect body are threaded with at least one end having a rotatable threaded sleeve adapted for connection to a tool module by a threaded collar. The ends of the interconnect body are adapted to receive seals for sealing each end of the interconnect body to a respective threaded collar when assembled to prevent thereby ingress of drilling mud into the hollow interconnect body. An interlock is provided at least at one end of the interconnect body with rotatable thread sleeve to engage the interconnect body with the tool module.

Abstract: The present invention provides a connector arrangement for connecting a first tubular to a second tubular. In particular, the present invention relates to a method for connecting tubulars in such a way that the connection is prevented from becoming unmade in response to expansion of the tubulars in a wellbore. More particularly, the present invention provides a tubular connection using a helical or spiral thread insert to seal and maintain mechanical strength in a tubular connection after expansion.

Abstract: An expandable threaded connection between segments of expandable tubulars that provides multiple sealing points along the pin and box members that can withstand high pressure is disclosed. The present invention utilizes a gap that is created between the pin nose and the back of the box member when the threaded connection is made up and a reverse trapping angle machined into the pin nose end and the back of the box. The radial expansion of the tubulars causes axial movement of the pin nose and the box member until the pin nose is in contact with the back of the box member, thereby closing the gap and forcing the pin nose into sealing engagement with the back of the box member. The reverse trapping angle forces the nose of the pin member outwardly (i.e., toward the outer diameter of the expandable tubular string) as it is forced into contact with the back of the box member during the expansion process.

Abstract: A submersible pump drop pipe and casing assembly and method of manufacture is disclosed. The drop pipe/casing has a seated connector and base. The seated connector has a first and second cylinder section, the first cylinder section being used to align and direct the base into the seated connector and to provide lateral strength to the pipe.

Abstract: A method and apparatus for providing an expandable threaded connection between segments of expandable tubulars is disclosed. Threaded connections are machined into pre-expanded ends of tubulars. Once the threaded connections are machined into the pre-expanded ends, two joints of tubulars are connected using the threads, thus creating a pre-expanded threaded connection. After a tubular string is made up and lowered into a wellbore, the entire length of the string is expanded using known methods for expanding tubulars. During the downhole expansion operation, the pre-expanded threaded connections experience minimal expansion. The minimal downhole expansion of the pre-expanded threaded connections allows the threaded connections to maintain their sealing ability and coupling strength.

Abstract: This invention relates to a threaded joint for steel pipes which comprises a pin and a box each having a contact surface including a threaded portion and an unthreaded metal contact portion and which guarantees galling resistance and gas tightness in a stable manner without application of a compound grease. A solid lubricating coating comprising a lubricating powder (e.g., molybdenum disulfide) and an organic or inorganic binder is formed on the contact surface of at least one of the pin and the box. The proportion of area of a cross section along the thickness of the solid lubricating coating which is occupied by secondary particles of the lubricating powder having an equivalent circular diameter of 15-60 &mgr;m is from 5-90%. Alternatively, the solid lubricating coating comprises, in addition to the lubricating powder, a fibrous filler (e.g., inorganic whiskers) in such an amount that the mass ratio of the fibrous filler to the binder is 0.01-0.5.

Abstract: A threaded connection for a conduit is disclosed. The connection includes a male member having threads on it defining a load flank lead, a stab flank lead and a nominal lead. A female member has threads thereon adapted to mate with the threads on the male member. The threads on the female member define a load flank lead, a stab flank lead and a nominal lead. At least one of the load flank lead and the stab flank lead, on at least one of the female member and the male member, is changed at a predetermined rate beginning at a selected distance from an end of the threads. The load lead and the stab lead are different from each other over at least part of the thread length.

Abstract: A threaded tubular connection has a box member including an internal thread, a pin member including an external thread engageable with the internal thread of the box member, and a protruding sealing surface disposed in the box member such that the pin member flexes radially inward upon passing the protruding sealing surface during make-up. The threaded tubular connection also has a recessed seal cavity disposed in the box member and a reverse angle shoulder at the pin nose that forces the pin member to flex radially outward into the recessed seal cavity of the box member upon final make-up. A method of forming a double flex seal for a tubular connection includes engaging an internal thread of a pin member with an external thread of a box member and flexing a pin nose of the pin member radially inward by passing the pin nose over a protruding sealing surface of the box member during make-up.

Abstract: A method of making up a pipe connection results in precise axial preload. The pipe connection has a box tubular member and a pin tubular member, each having mating threads and makeup shoulders. The designer determines a desired axial preload interference between the makeup shoulders. Based on this, the designer determines an increment of preload rotation required between the tubular members after initial contact of the makeup shoulders in order to achieve the desired axial preload interference. The tubular members are rotated relative to each other past the initial contact of the makeup shoulders for an amount equal to the increment of preload rotation determined.

Abstract: Blood lines for hemodialysis and other blood handling procedures may be reused by placing connectors intermediately along the length of the blood lines so that the lines can be disconnected to separate out reusable portions thereof. Specifically, the bulk of the blood lines used may comprise branchless lengths of tubing which are easily reusable, and may be cleaned and stored along with a dialyzer or similar device by connection to a conventional reuse machine. Also, the connectors on the blood lines which are reused may have first and second sealing surfaces. The first sealing surfaces are used in the connections made to form the blood line in its normal form for use. Then, during cleaning and sterilization for reuse, the reusable connectors can connect first and second lengths of blood lines together making use of a second sealing surface, in which the first sealing surfaces are exposed to cleaning/storing solution to cause cleaning and antibacterial action on the first sealing surfaces.

Abstract: A thread for expandable downhole tubular connections is disclosed. It features a locking pattern on the pin and box, which engages upon expansion of the connection. The locking pattern compensates for longitudinal shrinkage away from a torque shoulder, as a result of expansion. A resilient seal can be incorporated into the design with pin to box clearance disappearing around the seal as a result of expansion. Resilient seals can be used in tandem to trap atmospheric pressure between them. The wellbore hydrostatic pressure helps engage the locking feature by pushing the box into the pin, helped by the trapped low pressure between the seals.

Abstract: The oilfield tubular pin and box connection includes double shoulders 16, 22. An inner sleeve 18 engages the box at shoulder 20, and provides one of the two shoulders 16, 22 for engaging the pin. The pin bore optionally may be provided with a similar sleeve 24, thereby providing one of the shoulders for engaging the box. The sleeve 18 may be secured to the box shortly after its manufacture, or may be added as a retrofit to an existing box with a single shoulder.

Abstract: Threaded and coupled pipe connections are provided with a number of design features that increase resistance of the connection to fatigue failure from cyclical side loading. The features acting alone or in combination include the provision of a pin thread that is formed along a single taper and that vanishes at the surface of the pipe. The coupling engages the pin such that the threaded area of the coupling engages all of the pin threads and extends beyond the vanish point of the pin threads at the optimum coupling makeup position. The threads of the coupling and pipe may engage along both the stab and load flanks to distribute the side loading. The external surface of the coupling may be tapered from the center toward each coupling end to reduce the stiffness ratio of the connection, and the ends or faces of the coupling may be reduced in radial thickness to prevent coupling splitting.

Abstract: A method of joining two pipe ends, by forming male threads on an end of a first pipe with a steep taper angle, forming matching female threads on an end of a second pipe, and applying adhesive material to the threads before twisting the pipes to fully engage the male and female threads, thereby spreading the adhesive material across adjacent load-bearing surfaces of the threads. The threads have multiple start locations for thread engagement so that the pipe ends may be twisted to achieve full engagement in less than one full relative rotation. The male and female threads are formed with a squeeze angle between matching surfaces of the threads between 0.5 and 5.0 degrees. The finished joint provides immediate leak-tightness, and immediate tensile, compressive and torsional strength and does not protrude outside of the pipe profile.

Abstract: Male and female coupling members (120, 130) for a drill string (10) have abutment faces (122, 132), fitted with torque reducing rings (124, 135) of low-friction, material, and multi-start threads (140, 150), with higher lead angles ∝ than forconvention coupling threads, to enable uncoupling of the coupling members (120, 130) at reduced torque.

Abstract: A radially expandable tubular connection including a box member having an internal thread and a first seal surface and a pin member having an external thread and a second seal surface. The external thread threadedly engages the internal thread and the first and second seal surfaces form a metal-to-metal seal upon engagement of the seal surfaces. At least one groove is formed on an outer surface of the box member, and the at least one groove is shaped so that the box member radially deforms in a direction toward the pin member in a region near the metal-to-metal seal after radial plastic expansion of the pin and box members after engagement of the threads.

Abstract: An expandable threaded connection includes a first tubular member, a second tubular member and a threaded connection for coupling the tubular members that includes one or more sealing members.

Abstract: A screw-threaded joint for a pipe has a male portion (10) and a female portion (12), having complementary screw threads (11, 13). The male thread (11) extends to a position adjacent a complementary stop shoulder (18) on the female portion (12) having a recess of conical cross-section having a rounded apex. The recess is adapted to receive a head portion having a conical cross-section with a rounded apex, the radius of curvature of which is greater than that of the recess's apex providing a seal with improved stress dispersal properties upon application of torque. The wall (33) of the cone's in-use outwardly facing surface on the male portion (10) can subtend an angle of from 28-36° to the longitudinal axis of the pipe. The corresponding cone wall on the female portion can subtend an angle of from 28-38° with the same axis. The male portion (10) can comprise a second stress dispersing surface (41), concave in shape.

Abstract: A rotating inner member is used to drive a downhole tool housed within the hollow outer member of a dual-member drill string. The downhole tool preferably will be adapted to receive rotational energy from the inner member. In a preferred embodiment, the downhole tool is an electric generator connected to a downhole electric device. In another preferred embodiment the downhole tool is a mechanical transmission that uses the rotational energy from the inner member to drive a non-electric tool, such as a downhole hammer. This invention will increase the consistency and efficiency of downhole energy production.

Abstract: The gap L (mm) which is the smaller of the gap L1 (mm) between the crest 1a of a tapered male thread 1 and the root 2b of a tapered female thread 2, and the gap L2 (mm) between the root 1c of the tapered male thread 1 and the crest 2c of the tapered female thread 2, the load flank angle &agr;(°) and the stab flank angle &bgr;(°), and the axial gap &dgr;(mm) which forms in the widthwise direction and is the difference between the thread ridge width of the tapered male thread 1 and the thread valley width of the tapered female thread 2 threadingly engaged therewith have the following relationship

Abstract: Socket (7) to be fitted on a pipe (1) and, respectively, coupling piece for joining two pipes. The pipe is provided, close to the end thereof, with a stepped-down section (4) on which a screw thread (5) is made. The transition to the main diameter extends at somewhat of an angle. The socket is provided with a lead-in section (8) that is of at least the same length as the adjoining threaded section. The lead-in section is provided close to the free end with a conical section equipped to engage on the sloping transition section of the pipe.

Abstract: A pipe joint with a sleeve element, which has an internal thread, and with a spigot element, which has an external thread which can be screwed to said internal thread. One element has a constant pitch throughout and the other element, with two sections extending in each case from the ends of the threaded length is likewise provided with a constant pitch. The other element has more than two sections with a pitch which is constant within the section but is different from the first-mentioned element, it being the case that the pitch difference at least of one section is in the opposite direction, in terms of sign, to the rest of the sections. The pitch difference of one section is at least double that of the adjacent sections and in the screwed-together position, in the section with the large pitch difference, the thread play and the thread tolerances are compensated and the load flank of one corner tooth of this section, with the guide flank of the other corner tooth, produces the basic bracing.

Abstract: The surface areas available for absorbing compressive loading of a threaded connection are increased by increasing the engaged area of a torque shoulder in the connection and by reducing the spacing between the stab flanks of the threads. The areas are increased by increasing the dimensions of the components and by decreasing the machine tolerances permitted in manufacturing the components. The gap in the connection adjacent the torque shoulder is reduced so that the contact surface area of the torque shoulder is increased while the close proximity of the surrounding cylindrical walls of the connection reduces voids that can receive plastic deformation of the torque shoulder corners. The surfaces adjacent the torque shoulder are cylindrical in shape rather than being tapered to reduce machining costs and increase the speed of manufacture of the connection.

Abstract: A lubricating coating composition in which at least one basic lubricant selected from a basic sulfonate, a basic salicylate, and a basic phenate is dissolved in a volatile solvent is applied to the frictional surface of a box and a pin constituting a threaded joint for oil well pipes. The composition may further contain one or more of a thermoplastic resin powder, another lubricant, and an extreme pressure agent. The surface roughness of the frictional surfaces preferably has an Rmax in the range of 5-40 micrometers.

Abstract: An adapter and coupler assembly has two externally threaded adapters, one left-hand threaded and the other right-hand threaded, and an internally threaded coupler, one end left-hand threaded, the other end right-hand threaded. The coupler threadedly engages the two adapters simultaneously, tightening on both by rotating in one direction, providing a fluid-tight seal. Each adapter has the other end barbed for connection to hose. The coupler and the two adapters each have an external annular flange which is perforated to receive seizing wire or wire ties to prevent the components from unthreading. The coupler has a multi-sided barrel at its center, and the adapters have a multi-sided nut portion, to provide purchase by a wrench-type tool. Each component may also have a mark indicating the starting point of the thread, to facilitate engagement of the components. The assembly is especially useful in fluid-carrying systems of boats, recreational vehicles, and campers.

Abstract: A thread for expandable downhole tubular connections is disclosed. It features a locking pattern on the pin and box, which engages upon expansion of the connection. The locking pattern compensates for longitudinal shrinkage away from a torque shoulder, as a result of expansion. A resilient seal can be incorporated into the design with pin to box clearance disappearing around the seal as a result of expansion. Resilient seals can be used in tandem to trap atmospheric pressure between them. The wellbore hydrostatic pressure helps engage the locking feature by pushing the box into the pin, helped by the trapped low pressure between the seals.

Abstract: During conditions of use of a threaded joint comprising a box portion and a pin portion used to threadingly join oil well pipes, the stress acting on the outer surface of the box portion is prevented from exceeding the yield strength of the base metal of the joint, and the occurrence of stress corrosion in the joint portion is prevented. Specifically, the amount of thread interference T is controlled to be at most a specified value calculated as a function of the inner diameter D1 of the pin portion, the thread effective diameter D2 at the basic diameter position, the outer diameter D3 of the box portion, the internal pressure Pi, and the yield strength &sgr;y and Young's modulus E of the base metal. As a result, a threaded joint which is suitable for joining of oil well pipes can be provided.

Abstract: A tightening method for a special joint having unthreaded metal-to-metal sealing surfaces and unthreaded shoulder portions. By controlling the ratio of the tightening torque at the completion of tightening to the shouldering torque at the time when the unthreaded shoulder portions come into contact to be in the range of 1.25-20 and more preferably 1.4-10, sufficient gastightness can be guaranteed and plastic deformation due to overtightening can be prevented regardless of the type of pipe joint or the conditions of use. As a result, it can be widely utilized in the tightening of special joints used with oil well pipes even under the present state of increasingly severe oil well environments.

Abstract: A submersible pump drop pipe and casing assembly and method of manufacture is disclosed. The drop pipe/casing has a seated connector and base. The seated connector has a first and second cylinder section, the first cylinder section being used to align and direct the base into the seated connector and to provide lateral strength to the pipe.

Abstract: In a threaded joint for steel pipes comprising a pin and a box capable of mating with each other, the pin having an externally threaded portion and an unthreaded metal contact portion as a mating surface, and the box having an internally threaded portion and an unthreaded metal contact portion as a mating surface, the mating surface of at least one of the pin and the box is coated with a lower porous zinc or zinc alloy layer by blast plating and with an upper coating which is either a solid lubricating coating (comprising a lubricating powder in an organic or in organic binder) or a liquid, heavy metal powder-free coating (e.g., a liquid coating based on a highly basic organic acid metal salt such as a highly basic metal sulfonate).

Abstract: An elongated drive string assembly comprising a plurality of hollow sucker rods and a 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 hole in an oil well. Each hollow sucker rod has at least a first end comprising an internal female threaded surface engaging an external male threaded surface on a connecting element, such as a nipple. In order to further optimize the stress distribution between the elements, frustro-conical, non-symmetrical threads with a differential diametral taper are used. The torque shoulders have a maximized mean diameter and cross-sectional area to resist storing reactive torque in the drive string. The nipple preferably has a wall cross-section that increases towards the torque shoulders from each free end, to increase fatigue resistance.