Flask Holder helps to prevent sample melt back. It allows a small Fast-Freeze Flask Bottom containing the sample to be placed inside a larger Fast-Freeze Flask so that the vacuum surrounding the sample insulates it from the room atmosphere. Compatible with inner flasks 7542000 (40 ml) and 7542200 (80 ml) and outer flasks 7541100 (750 ml) and 7540900 (900 ml). Stainless steel. Flasks not included.