It is the conical hollow element or tapered hollow vertical portion of the gating system which helps to feed the molten metal initially through the path of gating system to mould cavity. It may be made out of core sand or it may be cut in cope portion of the sand mould. It makes easier for the ladle operator to direct the flow of molten metal from crucible to pouring basin and sprue.
It helps in maintaining the required rate of liquid metal flow. It reduces turbulence and vertexing at the sprue entrance. It also helps in separating dross, slag and foreign element etc. from molten metal before it enters the sprue.