A cap-free closable neck end for a filler neck of a tank of a motor vehicle, the cap-free closeable neck including an upper entry space forming an insertion region for a fuel nozzle and being surrounded by a side wall, a lower sealing flap arranged in the upper entry space and closing mechanism arranged above the lower sealing flap. The closing mechanism includes an upper filling opening and an upper cover, which in a closed state at least partially covers the upper filling opening and being embodied in such a manner that the upper cover is displaced by inserting an outlet pipe of a fuel nozzle into the upper entry space for releasing the upper filling opening so as to allow for the insertion of the outlet pipe through the upper filing opening and the lower sealing flap. When used for forming a protection against a filling with unsuitable fuel, the upper cover, in its closed state, is blocked by a locking element and wherein the locking element is embodied in such a manner that it is unlocked as a function of a type-specific shape of the outlet pipe of the fuel nozzle, only when the tank is filled with suitable fuel.