The invention relates to a ball screw and nut mechanism comprising a screw (14) and a threaded nut (12), the nut operating in conjunction with the screw (14) by means of balls (28) which can circulate in a bearing path (26) formed by the threads (22, 24) of the confronting bolt and nut, the nut being otherwise provided with at least one recirculating insert (32) inserted from an outer face (18 ) of the nut, in at least one cylindrical housing (30), which runs through the nut from the outer face (18) of the nut (12) to the nut thread (22), the recirculating insert (32) having a first end (34) with a ball transfer slot (36) facing the screw (14). according to the invention: the mechanism comprises a recirculation insert member retaining body (32) configured to hold the recirculation insert member within the housing, the recirculation insert member (32) has a second end with a bearing shoulder over a nut bearing strip (12), the second end of the recirculating insert (32) comprises an orientation spigot (38) having a predetermined angular position fixed with respect to the groove (36) In the case of a ball transfer device, the guide tang operating together with at least one guide relief (44) of the retaining body to secure a recirculating insert member orientation (32) within the housing, the orientation of the insert element being fixed such that the transfer groove (36) is adjusted to the rolling path.a invenção se refere a um mecanismo de parafuso e porca com esferas que compreende um parafuso (14) e uma porca (12) com filetes, a porca operando junto com o parafuso (14) por intermédio de esferas (28) que podem circular em um caminho de rolamento formado (26) pelos filetes (22, 24) do parafuso e da porca confrontantes, a porca sendo por outro lado provida de pelo menos um elemento de inserção (32) de recirculação inserido a partir de uma face externa (18) da porca, em pelo menos um alojamento (30) cilíndrico, que atravessa a porca da face externa (18) da porca (12) at
