Mobius Helix

The model is made from a single wire that wraps over and over itself. Each of the two main helices are made up of five smaller helices. If you like then you can put ball bearings on the inside of the main helices, in theory a 5mm ball bearing should be able to roll throughout the entire interior. In practise the steel print appears to warp slightly, meaning that the ball bearing gets stuck in some places but it still fits and looks cool.