Wide mouth design facilitates mixing, pipette access, sampling and filling. Unique flat bottom interior permits the use of a standard stir bar. The graduation line on the neck is sharp with permanent large yellow colored encryption with brighter appearance as supposed to traditional glassware with white markings. Flasks are calibrated 'To Contain' at Class A tolerances, per ASTM E288 specifications. Supplied with closed bottom Polyethylene or Standard Taper Glass stopper to fit in the ground neck.