Casting Sprue Wax with Reservoir - 12 gauge, green 50/Pk. Used to connect the wax model with the casting mold's opening. During burnout, the wax is eliminated to leave channels through which molten metal flows into the mold cavity. Using a Casting Sprue with Reservoir prevents localized shrinkage porosity. The Reservoir a piece of wax attached to the sprue former approximately 1 mm from the wax pattern.