These Erlenmeyer flasks feature heavy-duty rims to reduce chipping, white, permanent graduations, and large marking squares. Made from high-quality borosilicate tubing with a low coefficient of expansion. Borosilicate tubing also provides uniform wall thickness resulting in the optimum balance between thermal shock resistance and mechanical strength. This flask is ideal for making yeast starters, just boil your wort in the flask to sanitize the flask. Place the flask directly on a gas stove, then move it to an ice bath to chill! Not recommended for use with electric stove elements! Takes a #7 Stopper