A detachable fan holder for Anet A8. Should fit any extruder block that was designed to hold a 4cm fan on it.

Make sure you adjust the magnet holes using OpenSCAD. Just open the SCAD file, edit the "magnet_diam" variable, press F6 to compile the model and hit "»STL" to export the STL file.

Why did I remove the heatsink?

With a detachable design, the heatsink becomes pretty much useless - if you don't think so you should probably read some basic middle-school physics book. It would be like not having a fan at all: the heatsink doesn't touch any hot parts. Also, having the fan blow directly into the extruder block has the side effect of pushing any filament debris away, which is usually a good thing.