A self-locating star wheel system (10) for spacing bottles on a conveyor (71) in a packaging machine comprising a pair of star wheels (12, 14) with a hub (16) and cam (13) disposed between them and mounted on an arm (80) which moves them into the stream of bottles until the cam (13) engages a pair of rollers (32, 34) mounted at the ends of a U-shaped pivoting bracket (36) attached to the machine frame to control the lateral position of the star wheels (12, 14) with respect to the stream of bottles. The cam diameter is specific for a given size star wheel (12, 14) so that the proper positioning of the star wheel (12, 14) is achieved by the geometric relationship between the star wheel (12, 14) and the cam (13). The mechanism also functions as a safety feature by sending a stop signal to the machine when something, such as a down bottle (62), causes the star wheel (12, 14) to move away from the rollers (12, 14).