I made this to couple together the base and a 1-1/2" PVC pipe for the tower of my MKII 5W Wind Turbine. I left the hole through the middle to save material, print time and so you can route the wires out the bottom of the tower.
Find the turbine here: http://www.thingiverse.com/thing:2060281
In case you want to use it for something else, it is 2.01" outside diameter on the large end, and 1.5" outside diameter on the small end. and 3-7/8" tall
EDIT: I printed my first one out and it needed a bit of sanding to get it to fit into the base and tower. I uploaded a new, slightly smaller diameter, file that should require less post-print work to fit. (depending on your printer and settings)
20% infill should make this strong enough. I have not printed this yet to test the fitment, but measurements should be close enough. Maybe some slight sanding needed.