These Class A Pyrex® volumetric flasks have machine-blown bodies to which are sealed heavy-beaded, heavy-tubing necks, tooled for ST polyethylene stoppers. The linear high density polyethylene stoppers are made with a closed bottom to conform to ST stopper dimensions. For replacement stoppers see Cat.No. 1-7624. The graduation line is sharp and permanent and large white block letters make the inscription easy to read. 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.