Here at Top Bearings, we stock two different types of O-ring kits – a metric version and an imperial one. O-ring kits contain a selection of O-rings of different size so that you can ensure that you always have an appropriate one whenever you need it. Our kits contain either 380 or 400 different nitrile O-rings which will be of use in the majority of applications. O-rings serve as a barrier between two sealed surfaces. Sitting in a groove between two parts, they are compressed, forming a tight seal. They are found in all sorts of equipment and may need replacing from time to time.