These 50mL Class A PYREX®, volumetric flasks have machine-blown bodies to which are sealed heavy-beaded, heavy-tubing necks, tooled for No. 9 PTFE color-coded keyhole stoppers. For replacement stoppers see No. 7630. The graduation line is sharp and permanent. 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.