KIMAX® Volumetric Flasks with Glass Stoppers have a single graduation ring blasted on the neck, calibrated to contain. A ground glass stopper is supplied. Marking spots on all sizes. Sizes 5 mL and larger are designed from ASTM Specification E288, Class A unserialized requirements. The 1 and 2 mL sizes are test tube shaped and are calibrated to E237 tolerances.