I was about to spend more money on a hub than the stepper motor it was to be mounted on - then I found these plastic hubs. Strong enough for my project, and easy to drill out to the correct shaft size. Works great. Why can't someone make a low cost plastic shaft coupler as well?

I was looking for a 5 mm hub. Plenty of expensive ones around. This 3 mm hub is much better value for money, and can be drilled out to 5 mm. this is OK if you don't need great precision. Worked for me.