These heavy duty PYREX® conical centrifuge tubes are made with increased wall thickness for greater mechanical strength. In order to conform to outside diameter and overall length limitations imposed by centrifuge rotors and supports, it has been necessary to reduce the capacity of these heavy duty tubes. Graduations are with durable white enamel. The 10mL size is graduated upward from tip in 0.1mL divisions. The 40mL size is graduated in 0.5mL divisions to 10 mL, and from 10 to 40mL in 1mL divisions. The phenolic screw cap is fabricated of a resin which is specially formulated to resist the effects of temperature and steam.