Now, finally, I have found two cheap solutions to mount my studio flashes.
One, to mount it to Alutruss with a Half Coupler.
One, to mount the flash near the ground with a floor stand.
First, I drove to Cologne. There is a small company called “Abelz Filmzubehör” they offer various Spigots.
They also can build custom models for you. The most used way to mount a Studioflash is a 16mm spigot.
I bought two spigots with 10 mm internal thread.
Then I grabbed an old Warning triangle, tore off the foil and the reflectors. I drilled a hole in the middle, and mount the Spigot on the Stand. And ready… here is it: