Unknown Raised Flat Base
Open Comb

This is another "Adjustable" that uses the flexing of the blade to provide the tension. The difference here is that the handle has a internal notched ring, while the twist knob has a small protruding pin that clicks into them. The settings are repeatable by counting the number of clicks. (see the fifth image below)
It arived in a Rotbart tin with an image that is pretty close to what the razor actually looks like, but there are no manufacturers markings anywhere in the razor itself.

There is a post on a German forum which shows a small instruction pamphlet which, when translated by "Google" says:
With this razor, the blade can be adjusted for any beard growth. It is also recommended with a tightened blade pre-shave and shave sharply at notches 1, 2 or 3.

If anyone has more information, please contact me.

 

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How does it shave?
Actually surprisingly very well.

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The Repair

This arrived without the little adjuster "stop", spring and part holding it together.
The piece that holds everything together is actually a press fit cap, but because I needed to be able to undo everything, I figured that a small grub screw would work better.
I turned the two little brass pieces - the stop and the screw and then threaded the hole. I wanted to ensure that I was on the right track so the spring in the image was from a disgarded pen, which I kept trimming until I had the needed length. It has since been replaced with a suitable stainless steel spring.
It now works as I believe the manufacturer intended it to work.

Unknown RFB repair