Having shown it only to friends, I had been asked to also show this thing public. Well, since they are all lawfully owned I do not have any problems with doing so, therefore take note of the attached pictures.
It's a short walk through history, starting with the very first officially used at the very rear - Maxim for the M1903 rifle from WWI. Note that while the Maxim has a big nut remaining on the barrel and for installation requiring the frontsight to be slided out, the two for the K98k are clamped in a similar manner as the GewehrgranatgerÀt. And the Maxim features an offset bullet channel, while the other two have a central bullet channel.
The middle one is one for the rubber shims. It carries a chart on it's body where it tells you which rear sight setting you should use for which "real distance". I assume it was meant to be used with a special subsonic ammo. Worth mentioning with this piece, it uses a wrong direction threading and hence has also an arrow pointing in the direction it should be turned to open it. I believe this was due to the rubber shims, which are in fact touched and probably could otherwise cause unlocking itself due to the bullet spinning.
http://i251.photobucket.com/albums/g...xim/maxim1.jpg
http://i251.photobucket.com/albums/g...xim/maxim2.jpg
http://i251.photobucket.com/albums/g...xim/maxim3.jpg
http://i251.photobucket.com/albums/g...xim/maxim4.jpg