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 . <EOS>