The "small wheel" is a fork lock- a metal band tightens around the steering tube to lock the fork for leaning up against something without turning the wheel and falling down. It's a handy gadget! In German, one term is bandfesteller- I can't remember the other one. I'd like to put one on any bike I ride and have been looking for something similar that I could adapt.
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Yes, Andrew, you are totally right, it is a "Bandfeststeller = Sling Tigthener", also called "Steuerkopfsperre=Steering Head Lock".
Once the Sicherheitsniederrad (Lower Safety Bicycle) was established, the German bicycle industry adopted this gadget right until the end of WW2 - it was employed almost universally in the DACH-countries (Deutschland/Östereich/Schweiz =Germany/Austria/Switzerland) - I mean literally all manufactures used it, except on the racing models and some export versions.
This strange oddity actually makes it super easy to tell the age of an antique German bicycle - if it has a Feststeller, it is Pre-WWII
The origin of this gadget, as far as I know, relates to the English, just like the Safety Bicycle itself...
There were several versions of steering locks, but the one depicted on top was the most common one.
Here re a few examples (credit to "AltesRad.net" = "The Cabe")
Has any contraptions of this kind ever been featured on a US-bike ?