If you ever had a steering box apart then you've likely come across a ton of little ball bearings. These act as the thread for the ball screw. As the ball screw screws into the piston, the piston needs to move up and down within the steering box. But rather than try and cut threads into the piston, the balls are used so that the piston can be rebuilt and adjusted. What you may not know is that those little balls are different sizes and they must be measured and installed in a certain order.