Thanks for your help! Now it is working.
First I added a print fan, and started to print a bigger cube (5x5x5cm). But still, my Z dimension was off by around 0.8cm.
I found out, that my printer settings were wrong, I used the settings for an imperial threaded rod (I have a IE).
Now I did some prints for my cable chain holder. The pieces work but the printer isn’t perfect.
First, I had to up the current for my Z motor, but still I have the problem that the threaded rod sometimes blocks.
Then my bearings at the rollers for X and Y movement don’t always touch. Is there a modification, so I can adjust the pressure on the conduit?
The current setup works, so I maybe going to reprint the roller F. The printer I previously used wasn’t very precise and I used very little infill, so maybe the roller F aren’t rigid enough…