80mm fan to 3" tube

This is an adapter to mate a standard 80mm fan mount to a 3 inch (75mm) tube. There is a similar one here http://www.thingiverse.com/thing:16842, but it lacks the "neck" to more gently change the diameter. It probably doesn't make much difference, but I wanted to play with the FreeCAD "part sweep" feature anyway, so here is my version! :-)