Abstract: A knob positioning structure comprises a rotary switch shaft, to which a knob is mounted, the rotary switch being mounted in a depression in an enclosure, within which are formed detent points. A threaded hole is formed in the end of the shaft onto which the knob is to be mounted, and outer serrations are formed around the end of the shaft. The knob has a knob mounting screw hole through which a knob mounting screw can be passed, a knob stopper which mates with a detent point in the depression of the enclosure, and inner serrations, which mate with the outer serrations of the shaft. The knob is mounted to the shaft by inserting a knob mounting screw, via a spring, through the knob mounting screw hole and into the threaded hole in the shaft, enabling a sliding motion between the knob and the shaft in the direction of the shaft axis.