Device to join together vehicle body components

A first channel-shaped support (6) is provided in an essentially horizontal section of a side bodywork part (2) extending towards the outside of the vehicle. A second channel-shaped support (7) branches off from the first support in at least one region of the latter. The guide rail used to mount the bodywork part on the vehicle is provided with corresponding channel-shaped embossed regions. The mounting device is particularly suitable for mounting bodywork parts on the rear of the vehicle and is used to secure them to a guide rail, which is in turn secured to the main body of the vehicle and provided with a receiving arm for the bodywork parts.