Thin ceramic or sand core that is inserted in the riser at the point of attachment to the casting. This thin core heats quickly during the casting and solidification process and therefore prevents early freezing of the riser neck.
In this way, the necking facilitates removal of the riser from the casting during cleaning. The necking cross section must comply with the riser neck cross section calculated during riser design. (Fig. 2, Foseco Foundry Division Vesuvius GmbH)