Of course it is possible that this shutter you have has been a special order. But special orders cost extra, wherefore I thought it was less probable that the Rietzschel factory would pay extra for just 1 mm less diam. But of course it's possible.
Yes, I've heard about the leather friction brake disk, but never actually seen it. As you see from the new pricture, all you can see is a low cylinder, where the leather might possible hide. I will try to fix the loose back group tonight, and would like to try it out ofcourse (but pls. dont hold your breath, as I've much to attend to). Yes, it's the Type B.
I enclose a picture of another Koilos of this type. I think it's a size 0, the former is probably a size 1. This
View attachment 207059 View attachment 207060 type 0 has a mounting thread of about 28,5 mm, and luckily I have the mounting flange. The lens is a Collinear III 13,5 cm f.6,8. Lens and shutter is definitely in much less than perfect condition. But as I plan to use it on my Speed Graphic I think it will be ok.