referring to fig1 the hid lamp 1 illustrated comprises an outer envelope or jacket having a bulb portion 2 with reduced diameter tubular neck portion 3 and an internal discharge envelope or arc tube 4 . the arc tube depends by a hinge ( not illustrated ) from a support rod 5 extending the length of the bulb from stem 6 to anchoring dimple 7 in the dome end , and is locked in the transverse attitude by a ribbon hinge connector 8 . this mounting arrangement is fully described in copending application ser . no . 276 , 878 , filed june 24 , 1981 , of d . c . knecht assigned to the same assignee as this invention , and incorporated here by reference . a lamp base 9 attached to a cylindrical extender or collar 11 is fastened to the neck 3 . as best seen in fig2 the base comprises threaded metal shell 12 , end insulator 13 and eyelet or end contact 14 , together with polarizing locator 15 . the locator 15 is a length of metal rod , suitably iron or nickel - plated iron when the base shell is brass . it is welded lengthwise to the crest of the base thread , suitably at about the third full crest from the shoulder of the base shell . the welding preferably is made by multiple spot welds so that the length of the piece of rod and the number of spot welds determines the shear strength . i have found that a length of about 1 cm will easily accommodate 4 spot welds and give shear strength fully adequate for the purpose . the locator performs the same function as a conventional locating pin and assures a predetermined angular orientation of the lamp on its longitudinal axis when the locator is screwed home against the cooperating stop in the socket . in fig2 the base is shown screwed into a socket 16 of which the ceramic walls 17 have been cut open for illustrative purposes . the metal socket shell 18 is fastened to the bottom ceramic wall 19 . it is threaded in the same fashion as the lamp base but the threading has not been shaded in to simplify the illustration . there is enough clearance between the side walls 17 and shell 18 to allow the locator 15 to pass through when a base is screwed into the socket . the upper edge 21 of the socket shell is cut along a helix paralleling the threads for slightly more than 1 turn . where the helical edge laps itself a full turn , a notch 22 is cut into the thread step to serve as a stop for the locator 15 . the notch 22 in the socket shell leaves a downwardly reverting lip 23 protruding back over the lowermost portion of the upper edge 21 of the socket shell . the locator 15 preferably has an upwardly bent or turned leading end 24 as shown in fig3 which rises behind the reverting lip 23 . due to the upward pressure exerted on the base through eyelet connector 25 and its spring 26 , the interengagement of upwardly turned end 24 of the locator and reverting lip 23 of the notch produces a locking effect . the locking effect prevents loosening and disengagement of the lamp through vibration or accidental jarring . instead of a bent end , the locator 15 &# 39 ; may have its leading end expanded to a ball or disc shape 27 as shown in fig4 . a convenient set - up or jig for welding the locator to the base shell is illustrated in simplified form in fig1 . the lamp base is accommodated in a copper cradling electrode 28 while the lamp is rotated on its longitudinal axis until the arc tube is oriented vertically as shown . an optical system ( not shown ) providing an enlarged image of the arc tube on a screen may be used as an aid to rapid error - free orientation . a fixture comprising a small block 29 of insulating material such as a phenolic plastic , appropriately grooved on its underside to match the base threads , may be used to hold the locator piece 15 on the crest of the third thread of the base . a slot cut through the block overlies the thread crest and holds the locator piece 15 in place . a central enlargement in the slot permits penetration of a tack or spot welding electrode 30 from above . the block 29 is shown sectioned with one half removed for illustrative purposes in fig1 . the welding electrode depends from movable arm or actuator 31 coming out of spot welder 32 through which moderate pressure may be applied on the piece while tack welding . a hinged bracket ( not shown ) may be used to pivot and locate fixture block 29 on each new lamp base . after the first tack or spot weld has been made , fixture block 29 is swung out of the way and the operator rocks the lamp back and forth in cradling electrode 28 while making the additional spot welds desired . the heat and pressure developed during welding curves the locator piece 15 into conformance with the shell even though the piece may have been a straight pin initially . the preferred embodiment of the invention and the method and techniques used in making it have been described for illustrative purposes and the scope of the invention is to be limited by the following claims only .