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The mounting below is one I built several years ago. It took a while.
The finger points to a thrust bearing of a cross stitch plastic disk (approx 9" diameter) between the aluminum plates. There is another above the gear that is allows the motor drive to move the plate relative to the gear itself. The lower plastic disk works as a slewing clutch and there is no need for a lock on the axis allowing the scope to be moved without bothering the motor drive. There is a large ball bearing that sits in recesses of the upper and lower plates. The gear simply slides on its outer race and the hollow shaft welded to the upper polar plate is used to preload the thrust surfaces. I used the same design scheme on my 9" refractor and it has been used at very high powers during significant winds.
I also used the mounting when I photographed Hale Bopp.
