Nalgene 4000 Class B Polypropylene Volumetric Flasks with Screw Caps provide the accuracy of standard glass flasks combined with the break resistance of plastic. Gravimetrically calibrated individually TC/TD at 20°C. Printing is durable; won't wear off. Guaranteed to meet the Class B accuracy requirements of ASTM E288 and ISO Standard 384. No meniscus to confuse readings. Oval marking spot. F4240-3 has additional line at 203-mL level for BOD and DO determinations. Before autoclaving, set closure on top of the container without engaging the threads. Autoclavable.