Prior to vulcanizing a spin casting mold, a Center Plug is placed in the center of the lower rubber disc. After vulcanizing, the Center Plug is removed, and the resulting cavity forms the center sprue of the rubber mold. The Tekcast Center Plug, made from zinc, is a style preferred by many moldmakers, having slightly tapered sides and incorporating a hemisphere that forms a dome in the center of the bottom half of a rubber mold. This dome enhances the speed with which molten metal is distributed throughout a rubber mold. Both discs are 1 1/2” in diameter. Item 176-024 is ½” high, and item 176-025 is ¾” high. Made in USA.