John Rodgers asked about this in the bushcraft knife thread. I hope this clears it up. These are easy to make and work well.
It's just a series of thick leather disks with a wheel bearing imbedded in the center.
I had used the same piece of cowhide as I used for my Skookum Bush Tool sheath with the same beeswax paraffin mixture to weather proof, so they are a matched set.
Mac