u201c bead core positioning device u201d device 110 comprises an annular element 115 mounted by respective runners 116 to the sliding tracks 103 a in an alternative embodiment of apparatus 100 not shown instead of tracks 103 a and of runners 116 longitudinal guides extending from the side upright 104 parallel to the longitudinal screws 105 may be provided for allowing the axial sliding of device 110 preferably three longitudinal guides are provided in this case arranged at 120 u00b0 with respect to each other and thus one at each longitudinal screw 105 the annular element 115 in this case is slidingly coupled to the aforementioned longitudinal guides by respective sliding bushes a plurality of bead core positioning members 118 are mounted on the annular element 115 one of these is shown in detail in fig2 the positioning members 118 being arranged adjacent to each other in a circumferential direction and coaxially to axis x x of the forming support 50 each bead core positioning member 118 comprises a support portion 111 of the annular anchoring structure 10 a portion 112 for pushing the annular anchoring structure 10 arranged in a radially outer position to the support portion 111 and an arm 112 a integral with respect to the thrust portion 112 and intended for allowing the coupling of the positioning member 118 to the annular element 115 preferably the bead core positioning members are at least eight more preferably such members are sixteen or twenty four arms 112 a are radially and synchronously movable with respect to axis x x of the forming support 50 and thus in the two opposite ways of the direction indicated in fig1 and.