These heavy-duty Kimax® tubes with a standard taper bottom and a graduated scale are calibrated to contain. With top finish to accept a Standard Taper stopper. Scale and legend are printed in permanent red stain on the 13mL size and permanent brown stain on 50mL size. Marking spot is blasted on both sizes. Manufactured from 33 expansion, low extractable borosilicate glass conforming to USP Type I and ASTM E438, Type I, Class A requirements.