A container is provided with an outlet opening and an annular insert embedded in the container at the opening. The insert surrounds the opening and includes an inner circumferential surface that is exposed within the opening. The synthetic resin material of the body surrounds the insert except for the inner circumferential surface so that the insert is substantially embedded in the body at the opening. The inner circumferential surface of the insert is threaded to receive an outlet coupling, and seats are defined between the insert and the interior and exterior of the container. A mold is also provided for forming a container within which an insert is embedded. The mold includes an insert assembly having a support and a heat sink which are able to shear free from one another during cooling of the container within the mold.