Leitz Wetzlar Universal Viewfinder for Leica, vintage
This viewfinder is for a wide range of Leica lens.
The numbers on the viewfinder is 3.5 - 13.5, which is 35-135mm
This has been used.
I did not try it on a camera but I did look though the eyepiece and changed the numbers and it did change the view.
So it seems to be working, the real test will be on a Leica camera.
This does not have a serial number on it.
These were made from the late 1940s-1960s.
Please see photos for the condition, it is a little dirty and has some spotting on the hot shoes.