I have printed this Spool Holder for my M3D Printer. Because the printer was not that accurate with x and y axis, I had to slightly remove a little material with a file to make it fit on the spool. I used a 12x28x8mm bearing. ID=12mm, OD=28mm, Width=8 mm It works great on my M3D and the bearings are turning smoothly. I have drawed the spool holder with 123D Design. I have attached the source file, so you can customize it for your purpose. If you want to see more stuff, have a look at my Website: http://www.squirrel-crafts.com