Bushings are cushions made of rubber. They are mounted on car suspension and steering joints to absorb road bumps, control the amount of movement in the joints and reduce noise and vibration.
Without leaf springs to absorb the shock, you would feel every knock and jar from
every pothole or uneven road. This would cause the passengers to move with the
vehicle and feel every bump.
The center bolt assists in assembling, shipping and handling of the spring before
it is placed on the vehicle and holds the spring together for assembly and help locate the spring
onto the axle in the correct position.
Correctly tightened ubolts are what holds the springs firmly in place on the
vehicle when driving and prevent serious damage to the suspension
system or serious injury to the vehicle operator.