Floor Tool
A design similar to this floor tool was used on many European Hoover cleaners from around 1970. I say similar as it is not QUITE the same as the Hoover version - also it is not the correct tool for this cleaner, which would have been supplied with the "classic" floor too supplied from Hoover 862 (86) onwards. Also the Hoover version has a plastic rather than metal coupling.
As European Electrolux also used a flip over tool I think this may hhave been a generic replacement nozzle for both makes (its the red dot makes me think Electrolux) inspite of the Hoover logo which would have been over the area where the screw is.
Markus, you are lucky to have founds such a good example of this cleaner, although I think that perhaps you have another?
Al