Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1267183.
Bracket to hold a cooling fan (See Thing: http://www.thingiverse.com/thing:1161013 for the fan shroud) and inductive sensor on my Folger 2020 Prusa i3.
OpenSCAD file included but requires the .stl from: http://www.thingiverse.com/thing:1161013
Added new .STL and OpenSCAD files for an 18mm version. One about the same as the original 12mm but pulled in as close to the printhead as I could get it. And a second version I haven't printed yet with the ring pulled back in the Y axis so it will clear my binder clips better the bottom thickened for more strength and tried to make it look cleaner.
If you grabbed the new big-back.scad file before I'm putting this notice up - it probably won't work. I had to add a bit more clearance between the loop and the extruder. I've uploaded the replacement file and the print of it is what's shown installed in green.