Flask Boiling with joint 250ml, socket size 19/26, round bottom, interchangeable joint, single neck, borosilicate glass-EIS-CH0404F offers a thoughtfully designed, durable resource for hands-on learning. Made of high quality, heavy duty Borosilicate glass. 250ml capacity. Interchangeable screw thread joint. Socket size 24/29. Flask measures 5" tall and 3.25" width at the widest point. Perfect for any home, school, or professional science laboratory. 250ml capacity boiling flask made of high quality, heavy duty borosilicate glass. Interchangeable joint with socket size 24/29. Flask measures 5" tall and 3.25" width at the widest point. Eisco Labs Borosilicate glass has the following heat tolerances: Strain Point -515°C | Annealing Point 565°C | Softening Point 820°C.