Wikipedia: In mathematics, the Klein bottle is an example of a non-orientable surface; informally, it is a surface (a two-dimensional manifold) in which notions of left and right cannot be consistently defined. Other related non-orientable objects include the Möbius strip and the real projective plane.

It is also said that a glassblower does not become an expert until he/she can recreate this model.  I took that idea and decided that I would also treat it as a measure of my skill in CAD modeling.  Seeing as the original Klein model was surprisingly quite easy to recreate, I decided to take the difficulty of my test up a notch and combine three Klein bottles in one.

I also went ahead and 3D printed it because the model turned out great: