Calibrated "to contain" (TC) at 20°C, these Class A, borosilicate glass, wide mouth flasks are designed to provide pipette access along with facilitating filling and sampling. Unique flat bottom interior permits use of a standard stir bar. The heavy wall thickness gives greater durability. Supplied complete with glass Standard Taper pennyhead stopper. Scientists rely on the expertise and artistic skills of Wilmad-LabGlass' engineers and glass specialists to manufacture NMR and EPR consumables and laboratory glassware of the highest quality. Used daily in academia, healthcare and chemical, petroleum and other industrial applications, Wilmad offers 7000+ items as part of their standard catalog as well as custom fabrication for individual glassware, glass repair services and OEM glass parts.