This Walter's type crucible holder is made of black rubber and includes a glass funnel. It is designed to fit into flasks of 250 - 1000 mL capacity and holds 25 or 40 mL Gooch crucibles. The Walter's type holder fits into the neck of the flask, just as a stopper would. This creates an air tight seal and allows the vacuum to pull through the Gooch Crucible. Sold as: Each