A third order 3D Hilbert curve with 1.5 mm thickness & clearance. 2/8 blocks are rotated so that it forms a loop instead of an open curve.
See http://www.shapeways.com/model/108620/tiny_hilbert_cube_variation.html for a 1mm version and http://www.shapeways.com/model/109525/ for a 4th order 1mm version.
2.25 w x
2.25 d x
0.886 w x
0.886 d x