These Pyrex® Vista™ flat-bottom boiling flasks have full length outer ST 24/40 joints, but with shorter necks. Wall thicknesses are controlled to provide balance between thermal expansion and mechanical strength for greater shock resistance. The flat 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.