An adapter coupling device includes an adapter having a polygonal recess for receiving a bit therein and a radial hole is defined in an outer periphery of the adapter so as to receive a bead therein. For this purpose, in an emergency, the return line of the pedal travel simulator, which is connected to the brake fluid reservoir during normal operation, is separated from the unpressurized brake fluid reservoir and instead connected to the delivery side of the electrohydraulic pressure supply system or at least to the pressure accumulator of the electrohydraulic system. The reservoir intersects a V-groove formed through at least one wall of the body and forms an elongated aperture for dispensing the fluid therethrough.