The name says it all...
There are two objects in the Art of Illusion model: one has through-holes for screws; the other just has indentations to allow you to drill your own subsequent to manufacture. In the latter case you can put the holes in different places if you need, of course. Then again, you can just move the holes in the AoI design.
Don't forget to make this in your RepRap machine with the apex of the hole teardrops pointing upwards.
File:Coat-hook.aoi - The AoI file for the coat hook.
File:Coat-hook.stl - The STL file for the coat hook (this is the one with the through holes).