A method of mechanically securing a fastener (2, 400) to a first object, the method comprising the steps of: - Providing the first object comprising a thermoplastic material in a solid state; - Providing the fastener with a generally flat sheet portion (2, 401) having an edge, wherein the fastener comprises a fastening element; - Positioning the first object relative to the fastener to provide an assembly comprising the first object and the fastener, in which assembly the edge is in contact with the thermoplastic material, characterised in that: - While the edge is in contact with the thermoplastic material, coupling mechanical vibration energy into the assembly until a flow portion of the thermoplastic material due to friction heat generated between the edge and the thermoplastic material becomes flowable and flows around the edge to at least partially embed the edge in the thermoplastic material; - Stopping the mechanical vibration and causing the thermoplastic material to re-solidify, whereby the re-solidified thermoplastic material at least partially embedding the edge anchors the fastener in the first object; - wherein, in the step of providing the fastener, the fastener comprises a perforation (20, 403), with the edge running along the perforation and the sheet portion along the edge has a section projecting away from the sheet plane. - Providing the first object comprising a thermoplastic material in a solid state; - Providing the fastener with a generally flat sheet portion (2, 401) having an edge, wherein the fastener comprises a fastening element; - Positioning the first object relative to the fastener to provide an assembly comprising the first object and the fastener, in which assembly the edge is in contact with the thermoplastic material, characterised in that: - While the edge is in contact with the thermoplastic material, coupling mechanical vibration energy into the assembly until a flow portion of the thermoplastic material due to friction heat generated between the edge and the thermoplastic material becomes flowable and flows around the edge to at least partially embed the edge in the thermoplastic material; - Stopping the mechanical vibration and causing the thermoplastic material to re-solidify, whereby the re-solidified thermoplastic material at least partially embedding the edge anchors the fastener in the first object; - wherein, in the step of providing the fastener, the fastener comprises a perforation (20, 403), with the edge running along the perforation and the sheet portion along the edge has a section projecting away from the sheet plane. - While the edge is in contact with the thermoplastic material, coupling mechanical vibration energy into the assembly until a flow portion of the thermoplastic material due to friction heat generated between the edge and the thermoplastic material becomes flowable and flows around the edge to at least partially embed the edge in the thermoplastic material; - Stopping the mechanical vibration and causing the thermoplastic material to re-solidify, whereby the re-solidified thermoplastic material at least partially embedding the edge anchors the fastener in the first object; - wherein, in the step of providing the fastener, the fastener comprises a perforation (20, 403), with the edge running along the perforation and the sheet portion along the edge has a section projecting away from the sheet plane.