As i found no skadis mount for Fritzbox 7590 AX i build my own.

The mount slides into the back of the modem and fits tight. See the picture with red marking for correct positoning.

As it can be a bit difficult to slide it onto the mount when the mount is already assembled to the skadis board better mount in once to the modem before final assembly to ensure it fits correct.

The T-Clip original and further informations check: https://www.printables.com/model/256896-skadis-t-clip-system

Theres also a tool to mount the T-Clips but this one worked for me without: https://www.printables.com/model/626856-ikea-skadis-t-clip-tool