A ball joint is a suspension component that connects the control arm to the steering knuckle. A solid shaft is connected to a ball, which is located in a lubricated socket. The joint allows the suspension to move and for the front wheels to steer the car while still providing a solid attachment point for suspension components. It is a critical component as it frequently supports a large part of the vehicle’s weight on the suspension. In the 2005 recall, Toyota admitted that the ball joint may have been damaged during the component’s construction, but it has offered no explanation for the failures in this recall.