There are 2 linear rails with 2 cars (1 on each rail) for X, 2 linear rails with 4 cars (2 on each rail) for Y, and 4 rails with 4 cars (1 on each rail) for Z(2 rails on the front and 2 on the back). Best quality all genuine HIWIN ordered from motion constrained. It was the 4 Z linear rails that helped with the frame's rigidity and allowed me to remove the top cross brace from the frame. These 4 rails go a long way towards holding the frame square. It is these rails that control the Z banding and have kept it to a severe minimum. But removing the lower bearing and collars from the threaded rods will eliminate it.