Look like alphacool will be making changes to the design:

We respect the high attention that is given to the waterblock in the forums, and we have taken a deeper look into the concerns of the “OUT”-thread which look like “half-cut”. The “OUT”-thread is designed 100% in accordance to the German Industial Standard (DIN), and we can guarantee that there are no problems with fittings also if they that have a 7mm long thread.
Nevertheless, in respect to the discussion and the concerns of the forum users we have decided to change the top of the waterblock so that the thread will be best for fittings with 5mm long threads. This design-change will be made with next production series.