A demonstration inspired by this paragraph in the Wikipedia article on the Reuleaux triangle: "A Reuleaux triangle (along with all other curves of constant width) can roll but makes a poor wheel because it does not roll about a fixed center of rotation. An object on top of rollers with cross-sections that were Reuleaux triangles would roll smoothly and flatly, but an axle attached to Reuleaux triangle wheels would bounce up and down three times per revolution. This concept was used in a science fiction short story by Poul Anderson titled "The Three-Cornered Wheel."[6]" I find it amazing that rollers with a cross-sectional that is almost triangular can transport a load just like cylindrical rollers. Watch the video and be amazed: http://youtu.be/2CSpXSGFaes Make in Diamond Age PLA on an Ultimaker 1.Straightforward to make but do ensure that you lay down the spacer! The end stops are a press fit into the rollers. It's probably a good idea to make one and try it for fit, adjusting slightly in your slicer if necessary. For me, the end stops were quite tight and I made 2 drifts to help tapping them home with a hammer. The second drift comes in useful when you come to fit the second end stop in a roller (use it to protect the end that already has an end stop fitted).