A self-locating star wheel system for spacing bottles on a conveyor in a packaging machine comprising a pair of star wheels with a hub and cam disposed between them and mounted on an arm which moves them into the stream of bottles until the cam engages a pair of rollers mounted at the ends of a U-shaped pivoting bracket attached to the machine frame to control the lateral position of the star wheels with respect to the stream of bottles. The cam diameter is specific for a given size star wheel so that the proper positioning of the star wheel is achieved by the geometric relationship between the star wheel and the cam. The mechanism also functions as a safety feature by sending a stop signal to the machine when something, such as a down bottle, causes the star wheels move away from the rollers. The U-shaped pivoting bracket is spring loaded so that as the cam moves away from the rollers, the bracket pivots causing a metal block attached to the bracket to swing into position to activate a proximity sensor which sends the stop signal.