Well I printed one (took 3 days to print) and went out and bought some marbles today in anticipation of it's first run... and they don't fit, not even close. They were normal 'small' sized glass marbles (~15mm) but they are WAY too big. Not sure where I will find ball bearings the right size, so for now it's just a static ornament. Nice design and I was happy it fit's my 200x200x200 print area. Tough work on my old printer but it came out OK.