An apparatus for moulding a thermoplastic package part in association with an end portion of a packaging container body, the packaging container body including thermoplastic at least in an inner layer, the apparatus comprising: an inner mould element and an outer mould element between which a mould cavity is formed, the cavity being disposed to be able to receive at least said end portion of the packaging container body so that it is in contact with the cavity, and of which at least one of said mould elements (24, 26) is at least partly freely suspended, means for injecting a plastic melt in the cavity, means for converging said mould elements (24, 26) so that the cavity is closed and for applying a compression force on the mould elements (24, 26) for forcing out the plastic melt in the cavity, the compression force, as a result of the partly free suspension of at least one of the mould elements (24, 26), acting in a force centre, characterised in that the plastic melt is injected in a number > 1 of points in the cavity, an island of plastic melt for each point being formed inside the cavity, and where the distribution of said points is such that said force centre passes through a surface which is orthogonal to a direction of the compression force and which is delimited by parallel projections (45', 45") of a number of islands onto a plane which is orthogonal to a direction of the compression force and by a number of imaginary straight lines connecting the islands in such a manner that the surface is at its maximum, wherein freely suspended comprises at least one of the mould elements (24, 26) being suspended via a resilient element restricting the compression force on the mould elements (24, 26) in order to press out plastic melt in the cavity. an inner mould element and an outer mould element between which a mould cavity is formed, the cavity being disposed to be able to receive at least said end portion of the packaging container body so that it is in contact with the cavity, and of which at least one of said mould elements (24, 26) is at least partly freely suspended, means for injecting a plastic melt in the cavity, means for converging said mould elements (24, 26) so that the cavity is closed and for applying a compression force on the mould elements (24, 26) for forcing out the plastic melt in the cavity, the compression force, as a result of the partly free suspension of at least one of the mould elements (24, 26), acting in a force centre, characterised in that the plastic melt is injected in a number > 1 of points in the cavity, an island of plastic melt for each point being formed inside the cavity, and where the distribution of said points is such that said force centre passes through a surface which is orthogonal to a direction of the compression force and which is delimited by parallel projections (45', 45") of a number of islands onto a plane which is orthogonal to a direction of the compression force and by a number of imaginary straight lines connecting the islands in such a manner that the surface is at its maximum, wherein freely suspended comprises at least one of the mould elements (24, 26) being suspended via a resilient element restricting the compression force on the mould elements (24, 26) in order to press out plastic melt in the cavity.