An assembly including horological movement support, a motor plate of a timepiece and a fastener fastening the support to the plate. The fastener includes a self-tapping screw having a body that passes through a hole in the support. A recess in the plate or support is tapped when the screw is screwed into the recess. The shape of the recess has 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.