these are precision-made, high-strength tubes of glass or plastic made to fit exactly in rotor cavities. they may vary in capacity from 50 ml down to much smaller capacities used in microcentrifuges used extensively in molecular biology laboratories. microcentrifuges typically accommodate disposable plastic microcentrifuge tubes with capacities from 250 μl to 2.0 ml. centrifuge tubes with round bottom are moulded in polypropylene & poly carbonate. available in 15 & 50 ml. Capacity