A test tube holder's purpose is for holding test tubes in place, but they can also be useful for holding pipettes and stirring rods as well, and a test tube rack holds multiple test tubes in place. Some test tube racks can hold up to 40 test tubes. There are other racks designed for storing test tubes and holding even larger numbers of test tubes during a long period of time.
There are many different variations of test tube racks. These are also commonly referred to as test tube stands. They range in different materials, like wood and plastic, as well as their intended function. Some racks come equipped with spokes that allow the user to place cleaned test tubes upside down so they can dry out.
There are also many other accessories that are useful when using test tubes. Test tube brushes, for example, are essential for cleaning out dirty test tubes. There are also test tube clamps that protect the hands from having to hold test tubes that get very hot. Test tubes also sometimes use rubber stoppers that ensure the substances stay inside the test tube and allow the user to shake test tubes when needed. There are even wax pencils that are designed for writing on glass, which are perfect for marking test tubes.