Especially suitable for heavy-duty low speed rotary motion, rocking motion, and often under load and difficult to open and close a fluid lubricated parts; under boundary lubrication conditions can be long-term use without refueling and maintenance, refueling process allows the use of bearings Life can be more prolonged; their plastic layer on the surface of the molding process when the sleeve may leave some margin, after pressed into the openings can be self-processing, in order to achieve a better fitting size. Currently mainly used in metallurgical machinery, mining machinery, hydraulic machinery, automobile chassis, construction machinery, agricultural machinery, steel rolling machinery.