These Class A PYREX volumetric flasks are made from red low actinic stained glass to provide protection for materials sensitive to light. The protective color is an integral part of the flask, which retains its mechanical strength, chemical stability and thermal resistance. The graduation line is sharp and permanent and large white block letters make the inscription easy to read. These Class A volumetric flasks are calibrated to Class A tolerances in accordance with ASTM E-542 and E-288. Each flask is individually serialized and supplied with a Certificate of Identification and Capacity, traceable to NIST standards. For your convenience, these flasks are supplied with No. 9 Standard Taper red low actinic glass stoppers.