Universal Parametric Spool Holder v2

Largely inspired by http://www.thingiverse.com/thing:283656, but also by http://www.thingiverse.com/thing:971275 and http://micro3dfans.com/download/file.php?id=100&t=1&sid=dd6a0187c45290eb48d930511e0b8567, this design attempts to iterate forward a fraction.

The primary change over the original inspiration is the inclusion of space for 2mm washers either side of the bearing in order to fully trap the bearing but also preventing any friction from a connection with the side of the box. An furth