@Karl Clarke - Good morning and Happy New Year. Hopefully you and your family had a great holiday! I have been looking all around and cannot find the Fusion file that contains the internally splined "(1) Yoke Head Coupling Shaft x2" part for the Roll Channel with Metal Gears design. I am looking for this part so that I can increase the diameter and decrease the length (slightly) of its shaft such that it fits snugly into the original (Roll Channel plastic version) "(8) Head Coupling Shaft" part. My plans are to actually print the metal gears from that design so that I can use all of the "Roll Channel with Metal Gears" parts - without having the actual cost of buying the metal gears. The other reason I need to do this is that I have both heads already fully printed and fitted with the original gears and round coupling shafts. I am attaching a screen shot of what I am describing. Thank you so much for all you do for this hobby!!! Your work is absolutely amazing

Hello,
There is no design for the splined shaft for metal gears. I just had to go and get mine to check as this puzzled me. They are not splined but have grub screws that screw on to the shaft.
I would suggest printing the gears shown, and using the grub screws. It sounds like you are using the metal version, instead of building the dedicated plastic version which was designed to be all printed?
If you need more assistance please ask.
Kind regards Karl