Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2052951.

Spool adaptor to fit a hard drive bearing/motor. The internal diameter is 25mm for the bearing. The minimum spool internal diameter is 52mm. It would suit spools from about 54~65mm internal diameter. The overall external diameter is 80mm. The base is 5mm thick, and the overall height is 25mm.

Designed for use with this top mount spool holder bracket: http://www.thingiverse.com/thing:2054533

See also, this remixed version which adds slots for greater compatibility with different spools: https://www.thingiverse.com/thing:2340642