This is an adjustable standalone shower head holder. It's to be fastened to the wall with a single 5mm diameter screw. Adjustment is performed with the knob on the side.
The knob bolt is hex head M6, length from 25mm to 35mm.
This is an open-source design. FreeCAD file is provided.
Feel free to modify this thing at your convenience.
Good design is hard work, donations are welcome.