UPDATED: There are 2 versions of this design
This is a remix of https://www.thingiverse.com/thing:1746358.
Made by reverse engineering a printed version of http://www.thingiverse.com/thing:1746358 using a caliper.
I made this remix because I liked the original design, but it was extremely difficult to remix it using the *.step file provided for download. Hope that this remix makes things easier for editiing the design. That's why I've included the original FreeCAD file, used to design this THING.
Used 4 M3 x 10mm screws to hold the fan.
07/02/2017 - Version 1 of the design uploaded.
11/02/2017 - Version 2 of the design uploaded. This second version has a internal diameter larger than version 1. Version 1 has a 22mm internal diameter and version 2 has a 23mm internal diameter. This can be an issue with material retraction after printing.