Great work on this design, it is pretty awesome!
I happen to have a supply of 5/16" steel bearings. So for those interested, 5/16" is 83% of 3/8". So, I am printing with scale of 85%, which will cut several hours off the print time and fit the smaller balls I already have in stock. Incidentally, 5/16" is 7.93 mm, so the 85% scale should be good for 8 mm balls as well.