50mL round bottom, wide neck boiling flask made of lab-grade borosilicate 3.3 glass Inside diameter of mouth is 1-1/8" Diameter of flask bulb is 2" Thick beaded rim Used to hold liquid for heating/boiling or distillation This 50mL round bottom boiling flask is made from high-quality borosilicate glass appropriate for lab and classroom use. The inside diameter of the flask neck is 1-1/8", and the full bulb diameter is 2". Often used for boiling/heating liquids evenly, these flasks are commonly used in distillation setups. This flask is round on the bottom, and is most effective when held upright by a clamp on a stand, or placed in a cork ring on a level surface. Eisco Labs Borosilicate glass has the following heat tolerances: Strain Point -515°C | Annealing Point 565°C | Softening Point 820°C.