These Pyrex® Vista™ round-bottom boiling flasks have full length outer ST joints, but with shorter necks. They are manufactured from No. 7740 borosilicate glass. Wall thicknesses are controlled to provide balance between thermal expansion and mechanical strength for greater shock resistance. The round bottom boiling flasks are designed to ASTM E-1403. 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.