Updated- 01/11/12 gave a little more clearance and a little more chamfer to the fender.The nice machined side of a bearing is much more accurate than any printed part we can currently produce, so I'd rather not print a guide that encases the bearing. Instead, you can use these chamfered fenders instead of fender washers. They (hopefully) don't interfere with the spin of the bearing, but will keep the belt on track. The only problem with them is that the fender won't spin, so if the belt rubs, it will cause some friction. it's probably a good idea to coat them with some grease.These are designed to have a regular 8mm washer between the part and the bearing. Print 2 and put one on each side. you can use a fender washer if you'd like behind the printed part, or a regular washer.