A test tube rack is a laboratory equipment used to hold upright multiple test tubes at the same time. It is most commonly used when various different solutions are needed to work with simultaneously, for safety reasons, for safe storage of test tubes, and to ease the transport of multiple tubes. Test tube racks also ease the organization of test tubes and provide support for the test tubes being worked with. They come in a variety of sizes, compositions, materials, and colors, including metal wires, plastic, polystyrene, foam, fiberglass, and polypropylene. Test tube racks can be used in various circumstances, such as being placed in an autoclave or refrigerator.

In summary, a test tube rack is used for:

• Holding multiple test tubes upright at the same time
• Organizing test tubes
• Providing support for test tubes
• Safe storage of test tubes
• Transporting multiple test tubes
• Ease of use when working with multiple solutions simultaneously.