This convenient O-Ring Kit contains 30 of the most popular sizes, for a total of more than 400 O-Rings, in one convenient Kit. It is ready to use and will give you easy access and storage to whatever size you need. The storage posts are clearly labeled to provide instant size identification. There is even a built in gauge to measure the size of the old O-Ring needing replacements . this Kit is available in either high performance Viton, Buna-N composition.