An O-Ring is a mechanical gasket in round shaped used for packing & sealing, it is designed in such a way that it can fit in a groove and be compressed to give better sealing qualities.
O-Rings are the most preferred sealing component because of the low cost, ease to make & simple mounting requirements. They are manufactured through a process known as molding. O-Rings are available in various sizes the most common of them being AS568, BS & JIS2401 to name a few. The O-Ring size constitutes of two main dimensions: Inner Diameter (ID) & Cross Section (CS).