Test Tube Rack, 1-Piece, PP, 16Mm X 36 Tubes, Pack Of 4 One-piece molded racks have a three-tier grid design. Polypropylene construction provides good chemical and thermal resistance. Autoclavable. Racks feature a 3/4" x 2-3/4" labeling area on two sides. Open design allows easy viewing of contents from all sides.Available in sizes that hold 13mm or 16mm tubes. Both racks feature a 6 x 6 array of holes.