These caps have a mortice and tenon style connection. They fit together well and give you a place to add glue if you want.
This is a better version.
http://www.thingiverse.com/thing:1988435
Below is a link to my 2 spinners:
http://www.thingiverse.com/thing:1844145
http://www.thingiverse.com/thing:1842914
Cap_Bottom.STL | 102.6KB | |
Cap_Top.STL | 114.3KB |