Abstract: The knob comprises a body which cannot turn the control shaft unless the body is first pushed in. A brake prevents turning of the knob body when the body is in normal condition. Upon pushing the body rearwardly, the brake is disengaged to allow turning of the knob. Upon releasing the body, spring means projects the body forwardly back to normal condition in which the brake prevents the body from turning. Spring pressed balls allow the body to turn without turning the control shaft upon exerting excessive torque on the body to thereby prevent damage to the controls. Means is provided to limit turning of the control shaft to a predetermined angle.