This is a decorative monkey's fist knot. Compared to a standard monkey's fist, it is modified a little so as to be one endless knotted loop.
The bounding box of the "medium" size is actually a bit smaller than that of the "small" size, but the model is thicker overall.
This knot is available in several versions, differing in the cross section of the rope:
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Circle
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Square
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Twisted square
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Rope
- Rope with fine detail (that's this one)
Be warned that depending on material, size, wire thickness, detail, complexity of the knot and the mood of the guys who do the manual printability checks, Shapeways may refuse to print it. I obviously did not test this for all of my over 300 knot models. You can tell whether a knot has been printed successfully before in the chosen size and material by looking whether it says "first to try" under the material selection box.