An at least two shaft reactor/mixer, in particular for process engineering treatment of highly viscose, elastic and/or solid containing reaction substance and mixture, in which at the housing inner wall inwardly directed static mixing elements are arranged, which interact with scrapers of the at least two shafts in such a way, that in the area of the spaces between the scrapers the static mixing elements and the housing inner wall sheer forces, in particular a flow disturbance, are generated in an enhanced manner. In addition, there is a system including an end cap for a one or multiple shaft reactor/mixer and a discharge screw connector block being connectable with the end cap in a detachable manner.