Thanks to Michael Marsico, received?ProLock shaper spindle locking caps today. FWIW, there is an icon on top to indicate that the allen set/grub screw is the one to tighten.
I did not know how this gizmo works. The split screw that is hand tightened has a dome shape on the underside.
The cap has the negative profile. Once the screw is hand tightened I assume the two profiles marry/merge. Now as the allen grub screw is tightened the 2 halves of the screw spread. This should impart a downward force on the lower cap.
At least that is what I am theorizing after looking at it.