Abstract: The present invention relates to a system for retaining a cap with respect to the neck of a recipient. A bottle comprises a neck in which are hollowed two diametrically opposite grooves issuing from two top points and each terminating at a bottom point. The part of the grooves located above the top points is eliminated so that the bottom of said grooves opens out freely at the end of the neck. The bottoms of the ramps constituted by the two upper faces of the grooves are provided at their bottom points with a downwardly open notch. The cap comprises two fingers cooperating with the ramps to lock at the end of rotation in the notches. The invention is particularly applicable to the packaging industry.