Both the 96 and 64 Well "Reversible" Micro Tube Racks are designed so that one side of the rack accommodates 0.5ml microcentrifuge tubes. The reverse side holds 1.5ml to 2.0ml microcentrifuge tubes and screw cap microcentrifuge tubes. The clear polypropylene cover on the 96 and 64 Well "Reversible" Micro Tube Racks easily snaps on to keep it firmly in place during transportation and storage. A recessed area in the top of the covers allows for secure stacking of racks one on top of each other. The snap on cover is designed to accommodate the extra height of our Screw Cap Microcentrifuge Tubes. Two frosted writing areas for sample identification. They are autoclavable: 15 minutes, 15lbs. @ 120° C and will withstand freezer storage to -90°C. Alpha-numeric markings, "A" thru "H" vertically, 1 thru 8 horizontally.