1. Wax or metal used to form the hole or holes through which molten metal is poured into a heated mould.
2. The waste piece of metal that occupies the hole in the investment material when casting is completed. A sprue former ( sprue base, crucible former) is a cone-shaped base usually made of metal or resin to which the sprue is attached; it forms a crucible in the investment material which aids the passage of the molten metal during casting. A sprue pin is a solid or hollow length of metal used to attach the wax pattern to the sprue former.