SIBATA Class A, TC Micro Volumetric Flasks meet ASTM E-237 Class A, Style I Specifications. These flasks feature machine-blown bodies and heavy-beaded, heavy-tubing necks, tooled for ST stoppers. The graduation line is sharp and permanent; large, white, block-letters allow the labeling to be easily read. Both sizes feature hexagonal bases for added stability and are supplied with a glass ST stopper which provides a leakproof seal, depending on the liquid used.