Abstract: A knob arrangement for operating parking brakes intended for use in vehicles comprising brake units and an electrically operated tensioning means for applying or releasing braking force to said brake units. According to the invention, a means is arranged to sense the position of the knob and to send control signals to a first electric motor which is arranged to power said tensioning means for generating a braking force corresponding to the position of the knob. The knob is manually adjustable and, in a fully applied position, at maximum braking force, mechanically lockable. A control motor is arranged to automatically displace the knob to the fully applied and mechanically locked position dependent on second control signals applied to the motor. In its fully applied, locked position the knob is only releasable from the locked position by manual operation.