Racks are used to support, organize and store various types of glassware, labware and other items. Laboratory racks are available for pipets, test tubes, microtubes, vials, petri dishes, microplates, funnels, bottles, equipment, and instruments like thermometers or hydrometers. Racks may be made from a variety of materials, including plain or  epoxy-coated metal, wood, and various plastics. Racks for test tubes and microtubes have openings of various sizes to accommodate specific or a range of tube diameters, and some racks are designed for use with specific pieces of labware.