The early prototypes used roller bearings that are great for handling large loads, but proved to be unreliable in the long term. Production DHR's are fitted with large sealed bearings that should last a long time, especially due to the sealing and greasing system built in by Turner. The black pivot coverings are just that, caps that replace the bearing's dust shield and protect the bearings from the elements. In the center of the cap you'll find a removable grease port that lets you purge the bearing of any contaminants and force new clean grease in. Pretty nifty.