These 5mL Class A PYREX volumetric flasks have machine-blown bodies to which are sealed heavy-beaded, heavy-tubing necks, tooled for No. 8 Standard Taper polyethylene stoppers. The linear high density polyethylene stoppers are made with a closed bottom to conform to Standard Taper stopper dimensions. For replacement stoppers see No. 7624. 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.