height-adjustable holder for Anet A8 radial fan / filament cooler

After printing lots and lots of fan ducts and finding out that one is too short and cools the heat block down, another one is too long so it crashes into the heatbed, I decided to construct this thing to make the radial fan height-adjustable to use any fan duct I want. Assembly pretty much straight forward:

- Drop a nut in each of the two shafts of the back piece, don't worry, it doesn't get lost
- countersink the bore of the radial fan from the back side, the screw needs to fit in flat
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