Whilst upgrading my printer, I needed an effective way to tension my X Axis. I have made a few before, but this one is much more rigid, and uses less material than my previous designs. At the moment it does have a slightly wide slot for the pulley, but 2 - 3 washers will fix that, and give a little freedom for alignment. it uses 5-11-4 bearings MR115ZZ, or the fanged version MF115ZZ, the hole for the bearing is tight, which is good after all. print out at 100% fill, if required, drill out the TWO 11 mm holes, push M4 nut into buttress, for tension. CAUTION: drill slowly, making sure you cut both at the same angle of 0. Push the bearings in, slide in some 5 mm rod (cut down shanked 5 mm bolt) add pulley, tighten screws, print and get better quality prints :)