4-way rack stands on any of four sides to support different sizes of tubes. Holds the following combinations: four 50 ml tubes, twelve 15 ml tubes, thirty-two 1.5 or 2.0 ml tubes, or thirty-two 0.5 ml tubes. Racks can be joined together to support several sets of 50 and 15 ml tubes. Autoclavable polypropylene, one per pack. Measures 6" x 3" x 2 3/16".