Vessels are made to exacting tolerances to provide a higher yield and greater uniformity of cells per square centimeter. Glass tubing is specially selected for optical clarity, interior surface smoothness and general freedom from glass imperfections. Neck area is tapered to facilitate cleaning. Glass wall thickness is 2.6mm. Vessels and deep-skirted 38-415 screw caps can be autoclaved. Caps have white (styrene-butadiene) rubber liner. Nominal neck I.D. 29mm. Wheaton-33 low extractable borosilicate glass.