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Once I tighten, top stage doesn’t move.

Is the nylon tip mushroomed out, or too large diameter? The only problem it sounds like you're having is with the action of that knob. Maybe the thread is metric and not 10-32, giving you a false "tight" position?

Thanks Bob. I’m using a nylon tipped 10-32 set screw.

I've used these before. The knob isn't just a 10-32 screw. It has a shaped tip with a smaller diameter, if I remember correctly.

Thanks Joy.
Yes, it does seem counterintuitive! Just tried it with the knob tightened & nada. The fine adjustment must be broken as you speculated. I can push the whole lower micrometer & knob portion a few degrees with my fingers and it snaps back to the right - it’s feels like a very tight spring. I assumed it was cheap because it was sold minus the micrometer & the knob. The knob is a 10-32 screw which I had & I had a spare AJS micrometer which slides right in so I didn’t see it as an issue. Still a good deal for its purpose although a little clunky.
Thanks again.

PB = Peanut Butter Blaster... best lubricant ever... (LOL).
(Joy here). Ive used those, I have similar, and I can double check one when I get into work today.
The general idea is to loosen the knob to use the manual spin, but you must tighten it to use the fine micro. The issue is that is not quite intuitive, and people break them (did you wonder why it was cheap?) Often they just snap the positioning springs, with the effect that the fine adjust only goes in one direction and the other direction pushes loose. If they are frustrated (or curious like you) they try to take it open and yes, undo one of the set screws that hold the stage together. If you're only using it for a waveplate, dont worry about it - you got a real hefty piece for a deal.
Incidentally, if you're shopping for used opto-mechanno, I recommend http://www.lightglassoptics.com/

What is PB blaster?!

Soak it in PB blaster, or penetrating oil for a while ...

The micrometer itself is working fine. Already took it out and checked it. Seems to be the “tangentially driven high resolution outerstage” controlled by the micrometer, that’s not doing it’s job.

On most micrometers the entire head can be remove in its entirely , once removed soak it in penetrating oil ....