Summary

This is the simplest burr object, being 3 units long.

burr3.g is a brl-cad file.

http://www.research.ibm.com/BurrPuzzles/BurrInfo.html

Instructions

Print three. Have a small amount of fun fitting them together.

Actually, I designed this as a 1x1x3 cm test part to test for shrinkage.

It works well as is, but you might want to build it bigger if you want a real toy.
Also, this has no tolerances at all (since it was meant as a calibration part), and probably should have the middle section stretched a bit to make it fit. (I'll upload a fixed version too when I have time.)

burr3-1