Cap for a container, comprising a side wall extending about an axis (Z) and a transversal wall arranged at an end of the side wall , a separation line being provided on the side wall for defining: - a retaining ring intended to remain anchored to a neck of the container, which is configured to internally engage with an enlargement of the neck ; - a closure element which can removably engage the neck , so as to open or close the container; wherein the separation line extends about the axis (Z) and is circumferentially interrupted so as to leave a joining portion , between the retaining ring and the closure element , which extends circumferentially for a respective angle, the cap (1; 101) also having - an incision line (21; 21') which extends transversally to the axis (Z) between the separation line and a free edge of the retaining ring , so that two connecting bands are defined between the separation line and the incision line (21; 21'), the two connecting bands joining the retaining ring to the joining portion ; wherein - the connecting bands are deformable, for allowing the joining portion to rotate when the closure element is moved from a closed position to an open position, and wherein - the joining portion is externally provided with a projection which projects from the joining portion , characterized in that the projection is positioned between a separation plane in which the separation line lies, and the incision line (21; 21') so that, when the closure element is in the open position and the connecting bands keep the closure element connected to the retaining ring , an edge of the joining portion which, in the closed position, faces the retaining ring , is facing, in the open position, towards a rim of the neck and the projection is resting on the neck in said open position. - a retaining ring intended to remain anchored to a neck of the container, which is configured to internally engage with an enlargement of the neck ; - a closure element which can removably engage the neck , so as to open or close the container; wherein the separation line extends about the axis (Z) and is circumferentially interrupted so as to leave a joining portion , between the retaining ring and the closure element , which extends circumferentially for a respective angle, the cap (1; 101) also having - an incision line (21; 21') which extends transversally to the axis (Z) between the separation line and a free edge of the retaining ring , so that two connecting bands are defined between the separation line and the incision line (21; 21'), the two connecting bands joining the retaining ring to the joining portion ; wherein - the connecting bands are deformable, for allowing the joining portion to rotate when the closure element is moved from a closed position to an open position, and wherein - the joining portion is externally provided with a projection which projects from the joining portion , characterized in that the projection is positioned between a separation plane in which the separation line lies, and the incision line (21; 21') so that, when the closure element is in the open position and the connecting bands keep the closure element connected to the retaining ring , an edge of the joining portion which, in the closed position, faces the retaining ring , is facing, in the open position, towards a rim of the neck and the projection is resting on the neck in said open position. <EOS>