The oil seal (the popular name in CIS - salnik) serves for consolidation of shaft of rotary details and parts: shaft, yoke, lever, crankshaft, flywheel, gear wheel, transmission, reducer, wooble etc. Thanks to flexible edge from an inner bore which is in most cases drawn in by a spring, the seal held the lubricant by outflow  from a zone of bearing rotation.

Oil -seal is a rubber or polyurethane detail with the round bore, consisting of a metal-reinforced curved ring and the vast majority of cases -  spring-rings. There are over 20 types of oil seals, depending on the shape of their cross section. But the most popular are 2 type: TC and SC (one- or two edge). The popular name of oil-seal is SIMMERING.