Abstract: A plastic sealing ring is attached to a rim of a plastic container with an insert interposed between the rim and the sealing ring. By making the insert from a relatively rigid material, the insert can rigidify the sealing ring and hence the container. If the insert is made from an electrically conductive material, the insert can function to facilitate the induction welding of the sealing ring to the container. The sealing ring and insert can be formed as a unitary, composite sealing ring subassembly adapted for direct application to the rim of the container or they can be supplied as individual parts adapted to be applied to the rim of the container separately. In order to form the sealing ring subassembly, the sealing ring is molded from molten plastic. During the cooling of the sealing ring, the insert is positioned in a groove formed in the sealing ring.