This is a 20mm multi-piece marble that can be used in various games. The two halves are printed with no supports. The ring is not threaded and slides over the threaded piece which is then screwed into both sides of the sphere. This allows for customization of the ball without the need for a multi-color printer. 

The pieces can be scaled up or down for a specific size marble other than the 20mm size.  Use the Center ring for diameter size scaling first then scale the other pieces the same percentage.

The screw is a M12x1.75 thread.