You'll need 12 6mm x 2.6mm magnets to assemble the ring box.  You can get them on Amazon here Amazon.com: JARLINK 60 Pcs Refrigerator Magnets, Mini Premium Brushed Nickel Fridge Magnets, Multi-Use Small Round Magnets for Fridge, Dry Erase Board, Whiteboard at Home/Office/School (3 Different Sizes) : Home & Kitchen    

You'll also need to print 2 of the outer shell parts, 1 ring recess part, and 1 inner shell part.  Supports will be needed for the 2 outer shell parts.  I used tree supports when printing.