It is a pressing bar that is used for changing Impression Cylinder jackets. It supports the new jacket to the cylinder so that it can be secured at the tail edge. If you look at the tail end of the cylinder you will see threaded screw holes where the bar can be attached. In some cases customers want to mount different jackets for scoring, numbering or perforating. If you are not sure how it works, get trained Heidelberg techs to show you how it is used.