This 2-part hub mounts a standard CD or DVD on a 5 mm shaft. OpenSCAD file included in case you want a different diameter, change number of spokes, etc. File is tuned for my printer (Ultimaker 2) and likely needs adjustment for other printers if you want a tight fit. I also used some superglue.
Why do this? I am using a DVD just as a round shape, mounted on a stepper motor shaft, with an optical mouse looking at a strip of paper wrapped around the rim as a shaft encoder. This is to measure the rotation angle, to calibrate a microstepping driver. The python code to read data from a USB mouse is also included (on Debian Linux, anyway). My mouse has some drift over time, so this is not a good absolute angle encoder, but good enough for what I wanted.

EDIT: Surprised that quite a few downloaded this- I think my need for it was unusual. I wonder what other people are using this for?