is made of two portions of spheres, one inside the other. The outer ring can turn freely around the inner one.
The internal diameter is 20 mm (ask me if you need other dimensions). The inner ring can turn inside the outer shell (the clearance between the ring is 0.75mm, the thickness of each ring is 2 mm)
SUCESSFULLY PRINTED in Alumide. Unfortunatelly Metal is not possible (movable parts). A version with holes
(less expensive) is also available.
Very very addictive...