These Pyrex volumetric flasks provide improved lab convenience, broad selection and precise volume measurement. The strength of these flasks has been increased appreciably through machine-blown bodies to which are sealed heavy-tubing necks tooled for no. 13 standard taper glass stoppers. The graduation line is sharp and permanent and large white block letters make the inscription easy to read. These Class a volumetric flasks have been manufactured to Class a tolerances as established by ASTM E- 694 for volumetric ware, ASTM e-542 for calibration of volumetric ware and ASTM e-288 for volumetric flasks.