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They range in size from a couple inches to several inches long, from a few millimeters to a couple centimeters in diameter. They are designed to allow easy heating of samples, to be held in a flame, and often are made of expansion-resistant glasses, such as borosilicate glass (known by brand-names such as Pyrex and Kimax).
Tests tubes are often preferred above beakers when multiple small chemical or biological samples have to be handled and/or stored.
Vacutainers are a type of test tube that can be used for both collection and storage of blood.