This is a ball-chain pulley for 3.5mm ball chain, intended for use as part of a Polargraph:http://www.polargraph.co.uk/Regular metal ball-chain was easier to locate versus the type that Sandy had used on his Polargraph. I use a slightly modified version of Ed's stepper motor mounts as well:http://softsolder.com/2011/08/23/nema-17-stepper-motor-mount/The ball-chain I'm using came from here: http://www.kitkraft.biz/product.php?productid=8353&cat=&page=2Update: The gondola I printed for mine is here: http://www.thingiverse.com/thing:12557 - and it works!Pulley is sized for a 5mm shaft, and has a 3mm bolt / nut setup for tensioning on the shaft. If this doesn't match your stepper, edit the .scad file and change it up.