These 3 joints are made with nickel plated lamp balls. The balls are 3/8's in diameter, and largest ball that I use. The advantage of using this larger size is that the plates can be tightened down more for a stronger joint.

This photo shows the three basic joints that I use. The first joint (2-ball, single screw) is easy to make and works very well. If the holes are drilled out of alignment with each other, this joint will not work well. Also, the screw hole must be centered properly or the tension on the balls will be uneven. These two problems will happen sometimes, but more often I get excellent results.