Plug for a fluid coupling, corresponding valve, bottle and filling method

A stopper for fluid coupling of a valve of a pressurized fluid cylinder, the valve comprising a connector for filling with and withdrawing fluid, the stopper comprising;

• a self-locking sheath configured to slip onto a connector, the sheath extending about a central longitudinal axis, the sheath comprising, on an inner surface and at a first end, a tapped portion designed to engage with a mating threaded portion formed on an outer surface of a connector, wherein the tapped portion comprises at least one recess parallel to the longitudinal axis in projection according to a plane perpendicular to the longitudinal axis, the at least one recess being secant with the circle of smaller diameter of the tapping, and in that the inner surface of the sheath comprises, at a second end opposite the first end, a spindle extending inside the sheath in a direction parallel to the longitudinal axis towards the second end of the sheath as far as a free end located between the first and second ends of the sheath, the free end of the spindle configured to form a protective cover for a surface of the connector designed to engage with a filling tool, the free end of the spindle comprising a sealing member designed to press against a surface of a connector in order to create a seal, the sealing member of the free end of the sealing spindle comprising an O-ring housed in a circular groove formed on the free end of the spindle.