This flask is permanently marked with an individual serial number. Supplied with a Certificate of Graduation Accuracy. Graduation ring blasted on the neck. Calibrated to contain. With a marking spot. ST ground glass stopper is supplied with the flask. Cylindrical bodies allow for better mixing and drainage, and for ease in withdrawal of samples by pipet. Wide base (circular for sizes 1, 2, and 5mL and hexagonal for sizes 10 and 25mL) imparts much greater stability than is possible with a conventional shaped flask. The 1 to 5mL sizes are designed from recommendations published by the Committee on Microchemical Apparatus of the Analytical Division, American Chemical Society, "Analytical Chemistry", 28, page 1993 (Dec. 1956). All sizes have been designed from ASTM Specification E237, Class A serialized requirements.