I need to tighten my 21 clip and before I go off half cocked trying to unscrew the jewel I wanted to make sure that it does, in fact, unscrew! If not, how does it attach and does anyone have a tip for tightening the clip?

I unscrewed the jewel from my Parker 21 to tighten the clip, no problem.
I have to note that my pen it was (and is) Parker 21, not Parker Super 21. The later is very similar to 51 and I did not tried it yet.