Assembly the tool like shown on the picture, use as much M8 washer as you need for your wanted position (maybe print some of the other washer for better calibration they are 0,5,mm 1mm and 2mm ) .Do not use normal bearings with metalshield (like 608ZZ) as they will be scrap very soon after the chippings will get into the bearing.You don`t need to fix the M8 Screw with a nut like on landru`s original design, instead of this the bearings are fixed with the M3 screw (1 or 2 as you want to), so you can remove the screw without fiddle around with a wrench, after making the bolt just use a small file while the bolt is still in the tool and remove the material that is blocking the screw so you can remove it easily.Make a mark at the bolt at the position you want  (most used is 26mm? ), add as much washer as you need (for me 8washer and the 2mm printed washer fit), and make the bolt :)