A puzzle-sculpture in three parts.  The pieces are 3D prints in steel/bronze composite metal, and they interlock with 3/8" spheres.  It's held together by the inverse of tensegrity: compression forces hold the balls in place.

This piece ships with one set of balls in neoprene rubber, another set in frosted glass (pretty but a bit trickier to manage), and a wooden box to hold pieces and spare balls. 
 

Moon Pi, 3" diameter

This sculpture is made to order, please write for pricing or to request yours.

I use a rubber band to put this puzzle together (I'll send some bands of the right size), but that doesn't mean it's necessary.  I'm not very clever with puzzles!

 
Testimonials:

Lee Krasnow of Pacific Puzzle Works says, "It's darn hard."

Bjarne Jespersen writes, "It is not at all impossible – but not a piece of cake."