A plug of metal which is knocked out after an artifact is cast and which fits exactly into the opening (aperture or gate) of a mold. When casting metal into a bivalve or composite mold, the aperture through which the metal is poured into the mold becomes filled up with molten metal, and this plug of metal cools and hardens with the object. When the finished artifact is removed from the mold, the casting jet is still attached; in most cases it is knocked off and the scar polished down the metal plug being melted down for re-use. In some cases, however, it may be left on, particularly on neck rings and bracelets. Examples are sometimes in founder's hoards.