Weld the spherical joint to a bolt. This bolt will be used to connect to the top tube of the of the hitch arm. As noted previously, this ball joint is key to providing X-, Y- and Z-axis movement. My first hitch design allowed for only X- and Y-axis movement. The entire rig was very difficult to turn. Because the tow bike could not be leaned independently of the trailer, the trailer had a tendency to steer the tow bike.