There are usually around fifty bearings to be required for the basic operation of a tracked hydraulic excavator (travel & rotation).
Irrespective of its size and its use (earthwork, mining, demolition), it is made up of a crawler track chassis topped with a superstructure including the engine, hydraulic components (motors, pumps, cylinders), the driving cab and the attachment (arm, boom, bucket & dipper).
  
Travel
The two track sets are each driven by a planetary reducer using 2 angular contact ball bearings or tapered bearings - for supporting the reducer - and 14 needle roller bearings - for planet gears.
 
** 32 bearings are thus necessary so that the machine can move.
  
Swing
The superstructure pivots 360° thanks to a slewing ring of about 1.50 m diameter fixed on the straight truck chassis and a hydraulic motor or a planetary reducer. This includes 12 needle roller bearings for the planet gears & 2 spherical roller bearings for the shaft support.
 
**14 bearings contribute to the swing of the superstructure.
 
Note: The plain bearings equip the various joints located on the boom, the dipper and the bucket.