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 ST glass stoppers. The graduation line is sharp and permanent and large white block letters make the inscription easy to read. The 1mL and 2mL sizes are test tube shaped. Sizes 3L thru 6L have ST pennyhead stoppers. These 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.