These Pyrex® pear-shaped boiling flasks have full length outer ST joints and 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. 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. With short necks. Reusable.