Abstract: The stubs at the ends of the printing cylinder in a rotary printing press can roll along the upper surfaces of two arms each of which carries a plate with two mutually inclined upwardly diverging grooves for a pair of reciprocable stops. The stops can be shifted by cams to assume operative positions in which they flank the respective stubs and maintain them in predetermined positions for attachment of bearings to or for removal of bearings from the stubs. The stops are retractible to levels below the upper surfaces of the respective arms so as to allow for rolling of the stubs along the arms, either to advance the cylinder to its operative position or to roll the cylinder to a position in which it can be lifted off the arms. Detents are provided to yieldably hold the stops in selected positions.