Flasks are manufactured to conform to Federal Specifications NNN-F-289 for Type 1, Class “A” unserialized flasks and ASTM E-288. Supplied complete with one closed bottom polyethylene stopper. For additional stoppers, see CG-3018-P. NOTE: THE CG-1602-20 CONFORMS TO ISO 1042, DIN 12664 CLASS “A” FLASKS AND IS A Pyrex® PRODUCT.