A tubular frame section directly or indirectly attached to the vehicle and a mirror unit, attached by a clamping connection to the tubular frame section, whereby the mirror unit in interconnection to an adapter is attached to the tubular frame section. The adapter, which is torque-proof, displacement-resistant and coupleable with a fastening section of the mirror unit, can balance the diameter difference between the fastening section of the mirror unit and the tubular frame section. An inner contour of the adapter is designed so that the adapter can be connected in a form lock for the accurate attachment of the mirror unit to the tubular frame section in such a way that a longitudinal movement of the adapter on the tubular frame section is hindered and the degrees of freedom of the adapter are at least limited in the circumferential direction of the tubular frame section.