Polypropylene racks contain grids on both sides. One side holds 1.5/2.0ml microcentrifuge tubes with extra smaller positions for 0.5ml tubes, and the other side holds 0.5ml microcentrifuge tubes with extra positions for 1.5/2.0ml microcentrifuge tubes. The 96 place rack contains 12 x 8 arrays. The 80 place rack contains 16 x 5 arrays. Molded-in coding for easy indentifcation of tubes. Autoclavable.