Yep, that's the one.
. . .
- Is the loosening of the insert expected with normal use? I can totally see how it would loosen while putting the regs on and off the valves and it's trivial to check tightness when I assemble my rig. I don't usually do this as Deep6 are the only regs I have that have the removable insert. AFAIK, Apeks DST 1st stages don't have this.. . .
The DIN retainer (I think that's what this part is generally called) has loosened a couple of times on my HOG D1s as well. As I guess you know, avoid turning the reg itself when attaching the reg--hold the reg steady and turn only the plastic handwheel. Fortunately, I have a torque wrench to set the DIN retainer back to its proper tightness.