The design task for this project was to develop a mobile case carrying system for "Auer- System Koffer" for the company "toolbot". "toolbot" is an automated rental system for power tools with current locations in Berlin, Cottbus and Kassel. The product designed had to be as low-complexity as possible, universally applicable and inexpensive to manufacture. Consisting of a belt system and a folded sheet metal part, "Coat" represents my design on this topic. The add-on "encases" the tool case and inconspicuously creates a completely new usability. A rucksack for all case sizes from "Auer". The special shape of the add-on is created by twisting the inner dimensions of the case so that the carrying aid can be easily stowed in the case itself. "Coat" has been adopted by "toolbot" as a future mobility add-on and is already being produced in small series.