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.

Abstract: A threaded union highly resistant to overtorque and compression that includes a threaded member in its internal surface—called female—that joins a threaded member in its external surface—called male—. The union between the male extreme and the female is produced through the threaded surface. When the members are fully assembled, one axially oriented surface in the free extreme of one of the members—called nose—presses against a corresponding surface in the other member—called shoulder of torque. This shoulder is comprised of two surfaces, a first one coincidentally oriented to the corresponding nose of the first member, and a second one truncated and conical in shape with an angle B and with the axis of the pipe located between the first surface and the internal cylindrical surface of the female member.