I just realized why I made the profile so small on the hexagonal cut out was so it would fit the spool holder that comes with the cr-10 since there is such a small length of thread on the tube for the nut. oh and I forgot to say thank you for sharing your fusion file for the changer arm. I enjoy looking through the history to see how you designed it. It will be a good way to see how to utilize features of fusion together to make features of the part. The file is so clean compared to mine I hope to one day be able to design files that are that efficient.