Spool hub and holder. 52.5, 56.5 mm

This has been superseded by my much easier to use new design http://www.thingiverse.com/thing:550851

(UPDATED: Less filament use and additional hub size)
This hub allows you to change your spool without having to take all the nuts and bearings off. The slot allows it to be inserted into position on the rod and then insert the bearing to the hub and the hub to the spool, the nut is used to keep the hub in place. The bearing housing is 22.4mm to allow the bearing to be inserted/removed by