The present invention provides a sheet transfer cylinder for a rotary printing machine and has associated therewith a mechanism for gripping the sheets to be transferred and for turning same. The transfer cylinder is rotatably mounted in the side walls of the machine. One of the side walls is provided with a centering ring which is fixed relative to that side wall. The ring is provided with a pair of circular segments, one of which is adjustable circumferentially with respect to the ring. The transfer cylinder is provided with roller means which cooperate with the surfaces of said circular segments and which, in turn, cause the actuation of grippers carried by the transfer cylinder. Means are provided for regulating the degree of circumferential adjustment of the first of said circular segments.