That instruction describes how the parts can be repositioned to arrange the mics horizontally, one over the other, like in your photo. A custom spacer and threaded rod produces a greater spacing than you can get by doing that. The spacer goes in the middle, with all three parts on a longer threaded rod.
There must be photos on TS of this. It's usually done for X/Y LDs Maybe try seaching for the terms "vert" and "LD", since it's often referred to as a "Shure vert-bar".