Filler cap for tank

The tank cap (1) has a handgrip section (2) and engagement component (3) connected by a locking device which is constructed in such a way that in the screwing direction of the cap the handgrip section after overcoming a locking resistance can be screwed further with less rotational resistance. The locking device (22-27) has a single locking position, and a stop is provided to limit the rotational angle of the handgrip section after overcoming the locking resistance. The latter rotational angle is at least 10 degrees.