Abstract: Disclosed is a carton stop assembly for use in a machine which performs operations on a carton blank, and which includes a rotatable hub carrying a plurality of spaced radial mandrels, and insertion mechanism for telescopically inserting a carton blank over one of the mandrels. The carton stop assembly includes a track parallel to the one mandrel, having plurality of detents spaced therealong. An axially-reciprocable shaft has a first end overlying the one mandrel, and a second end overlying the track. The shaft carries track-engaging members at its second end, which enclose the detents on the track thereby stopping the shaft at a plurality of detent positions. A carton-engaging bracket is carried on the first end of the shaft and is arranged to overlie the one mandrel. As the shaft is reciprocated to a number of detent positions, the carton-engaging bracket is also placed at a number of positions along the mandrel.