toward lower base 34 the taper of frustoconical thread section 28 is substantial and is chosen to permit threaded section 28 to travel substantially into the mating threaded section in box 12 described hereinbelow before thread engagement begins nearest the lower end of pin 10 is a lower guide section 36 having a bevelled lower edge 38 guide section 36 is generally cylindrical in shape and like upper guide section 22 provides a flat to insure thread alignment in a manner hereinafter described the bore 20 of pin 10 comprises two cylindrical voids defined by walls 40 and 42 connected by a frustoconical void defined by wall 44 as shown void 42 is essentially the same diameter as bore 18 and is larger than void 40 void 40 is bevelled at its lower end 46 referring now to fig2 a box joint 12 for threaded mating with pin 10 of fig1 is shown box 12 is connected by means of weld metal 50 to a longitudinal member 52 which is tubular for casing applications on its exterior box 12 comprises a cylindrical weld section 54 which is essentially the same diameter as longitudinal member 52 and provides an area for welding to member 52 with weld metal 50 adjacent to weld section 54 and extending to the upper end of box 12 is a tubular end section 56 which is larger in diameter than section 54 and has a bevelled end 58 section 56 has in its interior threads for mating with threads 30 of pin 10 to be described hereinafter the transition from weld.