Abstract: Depleted stock feeder tubes, and feed malfunctions, are detected in bar fed machines such as automatic screw machines, CNC lathes and the like, employing reciprocating feed tubes with flexible feed fingers that grip the stock, with a sensor assembly mounted on a pivoted stock feeding lever or other feeder mechanism. The body of the sensor assembly is positioned to press against a roller or other connecting member extending laterally from the feed tube assembly, and retract the feed tube. A plunger or other reciprocating contact member is mounted in and biased to extend from the body. If a feed tube is stocked when the feed tube is retracted, the force required to retract the feed tube is greater than the biasing force on the plunger, the plunger moves, and a proximity sensor or other detector senses the new position or motion of the plunger.