What we do is drill and tap the 2 holes that were used for the recoil catches to 6mm x 1.0. Face and true up the flywheel after it is milled to remove the fins. We have a crank cut off that we clamp in the lathe to be sure and get the face perfect in relation to the crank. The hub we make for our 46's slids snugly over the origional flywheel nut and than the 2 6mm bolts hold it in place. If you look at the origional flywheel nut it has a sholder on it past the hex that is machined. That is what we use to locate the hub. We do not use the washer because it is not flat and will make the nut sit slightly crooked. By making the hub this way the entire crank takes the stress and not just the 8mm threaded end. We did have a crank snap off with a screw on hub. That is why we came up with this. On a smaller 25cc or so engine it is not a problem. Just on larger engines like the 46.