Abstract: A control device is disclosed operable by a rotatable control lever having an actuating cable attached thereto and received in a groove with a mechanism for determining index positions of the lever and for adjusting the radial distance between the bottom of at least a portion of the groove and an axis of rotation of the lever. The adjustment is accomplished by a chuck interposed between a support for the lever and connected to rotate with the lever. The chuck includes at least one projecting portion having variable cross sections adaped to engage in a cavity in the lever so as to constitute the bottom of the adjustable portion of the groove. The chuck is mounted to be axially movable relative to the support of the section of a control knob.