The strength of these Pyrex® flasks is increased by sealing machine-blown bodies to heavy-beaded, heavy-tubing necks, tooled for snap-cap fit. The graduation line is sharp and permanent and large white block letters make the inscription easy to read. The 2mL size is test tube shaped and does not have a snap cap. The 10mL through 2000mL sizes are supplied with blue snap-caps. For replacement snap-caps see Cat.No. 1-7666. 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.