This is a "mobius strip" but rather than being flat, has elliptical cross-section. The ratio of the ellipse's major to minor axis is 2:1.
I had one made out of black satin ceramic and am pleased with it. I think it's about the right size and weight for a pendant.
Because it's a curved surface, Shapeways need to add three mounting points on one side so that the piece could be supported in the fabricator. These are about 0.15 inches in diameter. I've not yet expeerimented with whether these can be sanded and polished out.