After building the fantasically designed MPCNC I needed a spindle. I bought a 500w spindle from China. I then designed this transition piece Spindle transition to tool holder for 23.5 model MPCNCin Openscad and printed it in PETG at 100% infill which is overkill but just a little more plastic, right? I designed it for 1/4" bolts and nuts, the metric ones are far too short. The only caveat to using it is to stop the the bolts on the tool holder side at the exact end of the 1/4" nut. There is some wiggle room but going too far will result in the bolt hitting the bearings. I actually just used 1/4" all thread to make my bolts and put a nylock nut on the spindle side.