Description General description Each individual flask′s measurement has been validated per ASTM E-542 during production, which guarantees conformance to Class A specifications called out in ASTM E-288. Each flask is labeled with "Verified" and a lot number. With this information, you can trace your glassware, access a Certificate of Analysis with lot specific data regarding both measurements and methods, and track usage. All flasks are supplied with both a Pyrex stopper and HDPE stopper. Legal Information Corning is a registered trademark of Corning, Inc. PYREX is a registered trademark of Corning, Inc.