This is a 3D printed piece that works as an interconnect between Duplo bricks from Lego and Brio wooden train tracks.
I was inspired by http://www.thingiverse.com/thing:4041, but after trying out a print, I found it too difficult for the 3 year old to put the tracks on, and I decided to make my own, slightly simpler design.
It's designed in OpenSCAD and I have uploaded the .scad file along with the .stl file, so that you can easily modify as needed
I have only tried to print these on an Ultimaker, and I have been printing without any kind of support.
After printing the brick with the Ultimaker (gcode made using skeinforge), I had to clear out a few extra plastic pieces from when the print head was moving between the different parts during pinting