In casting, the entrance hole and main channel in the wall of a mould through which the liquid material (bronze or other metal) is poured; it is joined to the model by smaller channels called gates. The waste material formed by the channel is also called sprue and is cut away after the investment material is removed, as the first step of cleaning up a cast metal sculpture.<br><br>In lost-wax casting, a channel through which molten metal can enter a mold (runners) and air and gas can escape (risers). This term applies to the wax rods attached to the wax model that result in the formation of these channels, and for the rods of metal that may be cast within channels once metal is put into the mold. In some regions, to attach the wax rods is called spruing, in others it is called rodding.Pictured here is a group of toy soldiers as they came from the mold in which they were cast. You may remember getting plastic toys in pieces, in the manner of these tiny soldiers (American, General Custer and His Troops). If so, you'll probably also recall removing the desired molded parts from the sprues that preserved the path through which liquid plastic reached the mold for each toy part. Here the sprue is the horizontal spine with a little tributary for each piece.