In early 90s I opened a bottle of coke, I took the ring that was holding the cap, I inverted the ring and put it on the cap. Now, when I have a 3d printer, I took 12 bottles and Autodesk Inventor...
This device has positive effect on blood circulation.
You will need 4 standard bottle caps and 12 under-cap rings from one famous company.
- Drill at least 5.5mm (6.0 at most) holes in the centers of the caps.
- Next, turn the rings inside out and put three of them on each cap. Those diameters match exaclty.
- Use 3D printer to make 1 holder, 1 axis and 2 inserts.
- Assemble, enjoy...