The copper-ceramic Mellow NF heat break is a great addition to an E3D V6 hotend. Sometimes though it can happen that the part that screws into the heatsink can rotate around the ceramic tube. This is easy to fix luckily and mentioned in their description too.

Supplies

16 mm spanner
7 mm spanner
E3D style heater block
E3D style nozzle
The Mellow heat break

Step 1: Installing the Nozzle

First insert the nozzle all the way into the heater block until it cannot go further. The orientation of the heater block is not important. After screwing it in back off the nozzle a little (about 1/2 a turn would be enough).

Step 2: Installing the Heat Break

Now screw in the Mellow heat break from the other side and all the way until it reaches the nozzle.

Step 3: Tightening

Now keep the heater block from rotating using the 16 mm spanner while putting the 7 mm spanner on the nozzle. Tighten the nozzle a little. Make sure not to overtighten it since the threads in the copper heat break can deform. Putting pressure on it with just an index finger should be good enough.