A quick-fastening element is provided for fastening a guide rail to two adjacent horizontally extending bars arranged in a vertically superposed and parallel relationship. The quick-fastening element has a first holding portion adapted for a positively locking engagement with a first horizontally extending bar of the two adjacent horizontally extending bars, a second holding portion adapted for a positively locking engagement with a second horizontally extending bar of the two adjacent horizontally extending bars, and a connecting portion between the first and second holding portions and connecting the first and second holding portions. Each of the first and second holding portions extends from the connecting portion to one side in angled relationship to the connecting portion fastenably between the two adjacent horizontally extending bars. The connecting portion is configured for fastening the guide rail.