BIBASE rubber support ring

Reversible; can also be stacked upon each other. Three sizes provide six different diameters for round-bottom flasks ranging from 50 to 6,000 mL. Excellent adhesion to glass prevents slippage and also offers thermal and electrical insulation. Available in two rubber types.
Black natural rubber − usable at temperatures from -20 to 70 °C (dry heat), -20 to 120 °C (moist heat), and has excellent chemical resistance.
Blue silicone − usable at temperatures from -20 to 200 °C. Withstands repeated high temperature or radiation. Physiologically non-toxic, biologically neutral.