These rotary shaft seals sit between rotating and stationary parts on a shaft to retain grease. They consist of a metal case that fits into a bore housing and a sealing lip made of an elastomer or rubber which presses against the surface of the shaft to create a seal. They do not have a garter spring which allows a slightly looser fit to the shaft, reducing friction and providing a more suitable seal for grease. Rotary shaft grease seals are often used in automotive engines, transmissions, and industrial machines that require the retention of grease in the housing of rotating parts.