I've designed this to securely fasten CreativeTool's Universal Filament Filter (http://www.thingiverse.com/thing:492067) onto the Printrbots extruder.

If you are confident in your printers overhang capabilities, print unsupported. You will need to take a knife to clear out the filament channel as I included a thin layer to make the bridging gap purely rectangular.

Orientate STL file cylinder side up on build plate.

I printed in PLA @ 195C
0.2mm layers
Orientated as the pictures show. (cylinder side up.)