Derick Gates SM2K #400 Brava
I had the same problem on Brava. The piece in your picture had frozen up, and I needed to take it to a rigger. The rigger was able to remove the inner tube from the outer tube, and clean and regrease it so that then it turned freely. If you then disengage the gearbox from the mizzen foil, you can remove it and see how the piece you have pictured screws into the gearbox. There are only a few threads between the two pieces. While you have the gearbox out, you can grease it too.
SM2K #400 Brava
Currently on the hard in Antigua