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

Print Settings

Rafts:

No

Supports:

No

Resolution:

.2

Infill:

100%

Notes:

I printed mine solid. Probably doesn't have to be.