This is a lampshade mount that converts a slip fitter to a threaded one. The base should fit most lamps, while the top is compatible with typical lampshade locking rings. A locking ring design is provided as well.
DISCLAIMER: You are dealing with electricity here and potentially high heat (especially if you are still using incandescents). If you kill yourself or burn your house and the local pub don't blame me! Use common sense.
Print the adapter flipped upside-down (narrow neck on the bed). The locking ring can be printed as is.
I've used OpenSCAD for this. I did my own parametric thread in 'thread.scad', which is simple enough to play with, but unlike something like this: http://www.thingiverse.com/thing:193647, it takes long time to render with CGAL and I don't know why. I'm new to OpenSCAD and any CAD for that matter.