Slotted Spool Hub - 2.25" Spool ID

This Thing is a spool hub designed for use on 5/16" (8mm) threaded rod. It is slotted to prevent the user from having to completely remove the nuts to change spools.

It was originally designed for use with 2ROBOTGUY's "SIMPLE SPOOL HOLDER FOR MENDEL" (http://www.thingiverse.com/thing:7982) but I'm sure it would work with other designs also.

Update:
I fixed the scale problem and also added an unslotted version. A slotted hub is really only necessary on one side. You could even lock the unslotted hub in place with a washer and nuts on the inside for simpler spool changes.