Volumetric flasks available in 4 sizes. Manufactured to Class A tolerances as established by ASTM E-694, ASTM E-542, and ASTM E-288. High quality inert 3.3 borosilicate glass. Flat bottom volumetric flask has a No. 27 standard taper ground stopper made from hollow glass, and a long neck style. Heavy Duty and reusable. Designed for great shock resistance.