first of all, please let me explain the unusual locking mechanism of this restraint for all, who are not familiar with it: if you turn the key clockwise, a small lever on the side of the lock-case can be turned to the right. If this lever is on the right side, you have to pull on the lock-case to open the cuff.
The movable (up to about 45 degrees, when cuff is in open position) part next to the lock-case is a little mystery. If it is moved "halfway", like shown on the second picture of my original posting, the cuff stays in open (neutral) position, but meanwhile I think that is just a coincidence and not the purpose of this part. My theory is that this "appendix" can be opened (only when the cuff is unlocked) to add a leading or belly chain or to chain several prisoners together, what is often needed in wartime (catchword: "POW").
Guenter aka Atame