I use bike chain for the axes of my reprap, and need to have a way to keep the chain staying on the jockey wheels of the Z-axis. This is only a problem for the Z-axis because the chain is horizontal and tries to fall off. For now I'm using polymorph rings (shown in picture), but wanted to make them look cooler. I haven't printed these yet, but the plan is that two of these can clip together and won't necessitate rebuilding anything. There's some terrible openscad code that makes the tab 0.95 times the size of the slot, so there should be space to fit.Print 2, clip together around z-axis, use a nut and washer to keep together.