These Pyrex® round-bottom boiling flasks have full length outer ST 24/40 joints, but with shorter necks. In addition, these flasks have a thermometer well with a ST 14/22 joint. They are manufactured from No. 7740 borosilicate glass. Wall thicknesses are carefully controlled to provide the proper balance between thermal expansion and mechanical strength for greater shock resistance. Their excellent chemical durability results in contamination-free results and long life under the toughest lab conditions. The normal working temperature for Pyrex® boiling flasks is 230°C. Adapter Cat.Nos. 1-8800, 1-8820 and 1-8825 are used to connect flasks with different size joints, thus allowing numerous combinations for diverse assemblies. Reusable. 19.5mm sidearm O.D.