An add-on part (10) for connecting to a component (30). The add-on part (10) has a longitudinal axis (A) and a welding section (11) to be welded to the component (30) by torsional ultrasonic welding. The welding section (11) has a contact surface (12) for contact with a torsion sonotrode (70) and a welding surface (13) for connecting to the component (30). The welding section (11) is delimited, at least in some sections, by an inner vibration-decoupling zone (14). The inner vibration-decoupling zone (14) extends, at least in some sections, at an inclination to or parallel to the longitudinal axis (A). The method comprises a) bringing the welding surface (13) in contact with a welding region (31), b) applying a force to the contact surface (12) such that the welding surface (13) is pressed against the welding region (31), and c) introducing a torsional ultrasonic vibration into the welding section.