Assembly comprising a support of a horological movement and a motor plate of a timepiece, in addition to means for fastening the support to the plate, the fastening means comprising: - a self-tapping screw configured to form a tapping when screwed, the screw comprising a head and a longitudinal body, the body comprising an end opposite the head and a threading arranged around the body, the body having a diameter that varies along the first axis of the body, which is wider at the head and extends to a smaller diameter at the end, - a first hole passing through the support or the plate, - a recess respectively arranged in the plate or the support according to the arrangement of the first hole, the recess having a shape defined by a wall and an opening for receiving the body of the screw, characterised in that the shape of the recess having a variable width, which is wider at the opening extending to a smaller diameter at the bottom of the recess, the shape corresponding to that of the body of the screw, such that, with the body of the screw passing through the first hole, the predefined shape of the recess is tapped when the screw is screwed into the recess, the body of the screw being cylindrical and comprising at least two cylindrical sections, a first section at the end of the body and a second section upstream of the first section, the second section being wider than the first section, and the recess comprising at least two cylindrical sections, a first section extending from the opening of the recess, and a second section located deeper inside the recess, the first section being wider than the second section. - a self-tapping screw configured to form a tapping when screwed, the screw comprising a head and a longitudinal body, the body comprising an end opposite the head and a threading arranged around the body, the body having a diameter that varies along the first axis of the body, which is wider at the head and extends to a smaller diameter at the end, - a first hole passing through the support or the plate, - a recess respectively arranged in the plate or the support according to the arrangement of the first hole, the recess having a shape defined by a wall and an opening for receiving the body of the screw, characterised in that the shape of the recess having a variable width, which is wider at the opening extending to a smaller diameter at the bottom of the recess, the shape corresponding to that of the body of the screw, such that, with the body of the screw passing through the first hole, the predefined shape of the recess is tapped when the screw is screwed into the recess, the body of the screw being cylindrical and comprising at least two cylindrical sections, a first section at the end of the body and a second section upstream of the first section, the second section being wider than the first section, and the recess comprising at least two cylindrical sections, a first section extending from the opening of the recess, and a second section located deeper inside the recess, the first section being wider than the second section. such that, with the body of the screw passing through the first hole, the predefined shape of the recess is tapped when the screw is screwed into the recess, the body of the screw being cylindrical and comprising at least two cylindrical sections, a first section at the end of the body and a second section upstream of the first section, the second section being wider than the first section, and the recess comprising at least two cylindrical sections, a first section extending from the opening of the recess, and a second section located deeper inside the recess, the first section being wider than the second section.