Do you have a spool that you want to mount on an axel that is too small for it? This .scad file lets you quickly make a set of two printable "bearings" that will center your spool on your skinny axel.

Measure your axel diameter, and the diameter of the center hole of your spool. The spacer acts as an end cap, to keep the adapters from sliding past the outer edge of the spool, but are also handy for centering spools.

This was originally designed for adapting spools to (and centering them on) a tinkertoy spool holder: http://www.thingiverse.com/thing:66975