These round floating bubble racks are specifically designed for incubation. The hold-down disk maintains a constant pressure on the tube caps, preventing them from opening under internal air expansion. A 4.8mm (3/16") thick polypropylene disk is centrally mounted on a threaded handle. The racks float, and 1.5mL microcentrifuge tubes remain immersed at a constant depth regardless of water level. The foam-filled TPX™ (polymethylpentene) rack and polypropylene cover plate and handle are steam autoclavable at 121°C. Racks have 19mm (3/4") long legs.