The first to use 13/16″ ball bearings. They are more forgiving if the track is too wide/thin but sharp corners demonstrate Newton’s Third Law nicely as there is a definite movement of the whole sculpture on the table. I like the ending as there is a Newton’s cradle affect. I sanded this one as I went along so it is a lot cleaner looking. It was the last one of my Christmas Holidays 2008/2009 as I get distracted by them once I start and don’t get much work done!