I liked the design of ONI Roller by 5quig, but the fit was too tight. This design is a bit shorter (to be more like AA batteries you can roll in your hand), and I placed small bumps on the contact surfaces between the plastic and bearings to provide a tight fit that's still pretty easy take apart and put back together.

I've created a few of these to give to people, but I don't have one on hand right now to post photos of.
The jury is still out on durability.

I created this in OnShape. I've posted the STEP files, or feel free to access the OnShape document here.

Hardware

• regular 608 bearings (4)