Expansible plunger; an attachment unit and a method for attaching a container element in a container body

An expansible press plunger:

• the expansible press plunger extending in an axial direction and in a radial direction perpendicular to the axial direction, the expansible press plunger being expansible in the radial direction, the expansible press plunger comprising:
• a base plate;
• a first plunger skirt,
• wherein the base plate comprises a bottom surface with a circumferential edge defining a shape of the bottom surface and a guiding surface opposite the bottom surface, and
• wherein the first plunger skirt comprises a top end, a bottom end, and a circumferential edge portion at the bottom end of the first plunger skirt, the circumferential edge portion of the first plunger skirt being arranged at the guiding surface of the base plate, the first plunger skirt being resiliently transformable between an unexpanded state and a radially expanded state;
• and
• a second plunger skirt, wherein the second plunger skirt comprises a top end, a bottom end, and a plunger skirt side wall having an inner surface and an outer surface, the plunger skirt side wall extending from the top end to the bottom end of the second plunger skirt, the plunger skirt side wall comprising a circumferential edge portion at the bottom end of the second plunger skirt, the circumferential edge portion of the second plunger skirt being arranged radially outward of the circumferential edge portion of the first plunger skirt, the second plunger skirt being resiliently transformable between an unexpanded state and a radially expanded state;
• wherein the first plunger skirt slides in a downward and outward direction on the guiding surface to bias the circumferential edge portion of the first plunger skirt against the inner surface of the plunger skirt side wall of the second plunger skirt when the second plunger skirt is transformed to the radially expanded state.