Use two roller skate bearings (608) to make a rolling cylinder! This is parametric, so you can use OpenSCAD to change the size and shape.

Useful for making pulleys, spools for plastic filament or thread, your own rolling pin, a rolling back massager, DIY skates, toy cars, a conveyer belt, tank treads, whatever!

You print it as two separate pieces and then put them together.

Tools
3D printer. I used a Makerbot Replicator.

Materials
male side (1) - 3D printed
female side (1) - 3D printed
608 Roller Skate Bearings (2) - I used Bones brand "Reds", findable on Amazon
5/16" or 8mm threaded bolt, any length (1) - Home Depot etc. will have them
5/16" or 8mm nut or wing nut (1)

Printing
There are two example STLs provided. I'd recommend printing those first, as they are small, and you can test-fit the components. Make sure the two parts fit together, and make sure the bearings will fit into the ends.

The male side will need support, since it has an overhang on the inside. The female side doesn't need support.

Assembling
Put some hot glue or epoxy on the male side, and plug it into the female side. Push a bearing into each end. Put a bolt through the whole thing and secure it with a nut. (See assembling picture.)

You may find that removing the rubber seals from the bearings reduces friction. There's a youtube video on how to do it here: http://www.youtube.com/watch?v=AXmZhfvH9y0

Make it your own!
In the OpenSCAD file, you'll find lots of comments about how to change the object to fit your application. Note that the single OpenSCAD file generates both the male and female STLs.

Enjoy!