These reusable PYREX® pipets are color-coded by size for easy identification and sorting. Colored graduations are enameled onto the glass. The top end of 5 to 25mL sizes is constricted (Mohr type). They are calibrated "to deliver" (TD) their total capacity without blow-out. Reference: ASTM E-1293. Do not pipet by mouth; we suggest using a mechanical pipetting device.