Voice andor image data packets are transferred by a packet handler between user stations in a GSM-type mobile communications system using a General Packet Radio Service data link. The impeller is mounted on the shaft by means of an internally-threaded insert, for example also of steel, interference fitted into the impeller hub. The tool box includes a box body defining an accommodation space having an opening which opens the accommodation space outwards and allows a tool to be put into and taken from the accommodation space through the opening, and an openingclosing cover which opens and closes the opening.