Do you find it useful what I made? Your can show your appreciation by taking a photo and upload it as an "i made one"! That would be awesome! :)
The ball in this keychaine is 12mm in diameter.
I juist added the bal in mid print.
Based on the coin trap.
http://www.123dapp.com/123D_Design/knikker-doosje-2/2381130

My reply to an email ;

Hello!
Thank you very much!
I drew it once (many years ago) in a program called 123D Design Online. Sadly, Autodesk has has stopped supporting that program and deleted everything. So I can't share you the files anymore :(.

In the files you could see how I drew the ring. The program was based upon dragging and dropping geometric shapes (much like thinkercad). The program was so fancy that later you could chamfer everything to make it smooth.

How to prevent the extruder bumping in the marble? Make sure the hight of the box is at a point where the printed box is higher than the marble. (at least one mm). Back then I had to get it right in one try because there was no pause function on the printer or software. Now you have so use it to determine if the print is high enaugh. Also, search for the right marble and if necessary scale the box for the best fit.