Flask Boiling - Florence, flat bottom, wide neck with beaded rim 500ml, borosilicate glass-EIS-CH0411D offers a thoughtfully designed, durable resource for hands-on learning. Flask made of heavy duty borosilicate glass. Flat bottom design allows for placing on tables or other surfaces. Not designed for measuring as there are no graduations. Stopper not included with item Premium flat bottom, wide neck boiling flask made of Borosilicate 3.3 glass. 500mL capacity. Flask neck has an inner diameter of 45mm, and an outer diameter of 53mm. Fits #10 Stopper (CH0321Q, CH0321Q1H, CH0321Q2H). Eisco Labs Borosilicate glass has the following heat tolerances: Strain Point -515°C | Annealing Point 565°C | Softening Point 820°C.