Abstract: A cap, in particular a tank cap, has a handle part for manipulating the cap upon screwing into and out of a neck, and has an engagement part for engagement of the cap in the neck. The handle part and engagement part are connected via a detent device that is embodied in such a way that in the screwing-in direction, after a detent resistance is overcome it allows the handle part to continue rotating out of a detent position relative to the engagement part with decreased rotation resistance. The detent device comprises only a single detent position; and a stop is provided for limiting the rotation angle of the handle part after the detent resistance is overcome.