Plane bearings can be integral, that is, the shaft sits directly on the groove. or as a form of bushing in which a semicylindrical sleeve is placed below the shaft. This has the advantage of being replaced when it worn. The sleeve is made of soft material as compared to the shaft.
Some plane bearings have two shells or sleeves. One above the shaft and one below. These bearings are used in the crankshaft of the engine.