The mountng rubber is a shock absorbing item that tempers the excitation forces of the vibrator units. While the rubber is highly durable, over time it is ultimately a soft material compared to metal that needs replacing after the fatigue of usage.
 
This item is also used on the Hyperstat and the Jumbo brick machine static adaptors to isolate the pallet tray from the frame; as well as on the vibration tables to keep the vibrational plate in place.