Bearing cap for the simple filament spool stand

http://www.thingiverse.com/thing:281848 is my favorite spool stand. I used horizontal spool stand (http://www.thingiverse.com/thing:508896) before and while it's good the horizontal spool stands have the problem when the spool winding is not smooth and that ends up in tangling. But with the vertical spool stands, the gravity works in their favor and not prone to tangling at all. One issue I had with the current spool is that the bearings would fall off easily. So, I created a simple cap for them