Abstract: A device is disclosed for use with adjustable rotary controls such as potentiometers to provide a means for locking the control knob and to provide varying amounts of drag force to aid in fine adjustments. A locking shoe assembly having integral locking shoes with cam surfaces is attached to the control panel with the rotary control shaft extending through its center. A locking knob with internal cams fits over the locking shoe assembly. A control knob with an integral land surface is attached to the rotary shaft, holds the locking knob in place and extends into the locking shoe assembly. Rotation of the locking knob engages the various cam surfaces thus binding the land surface and the control knob.