German Z.s.u.m.W.M. variations

[MINENAZ16]

Hello,
German made ZsumWM with different materials (brass, zamac, aluminium, etc) and graduations could change, 21 or 25 but it's the first time I see a small detail.
The small stopper on the graduated ring could be rounded or square, and screwed inside or outside the ring, brass or steel.

 

[Alpini]

One more type - a early 1915 Rheinmetall Z.m.W.M. (left) - is completely without the "stopper". A little bit later but in the same year made Z.s.u.m.W.M. also from Rheinmetall has the stopper. (right, only the groove for the stopper is visible in the picture)