I'm printing the parts for Harri678's case collator conversion using a JYG-370 10rpm motor. I'm assembling an entire new bullet feeder for this project. Here are a few pics of the coupler I used for this project.
The coupler I have is 6mm inside diameter on each end, 9mm outside diameter, I used a m3x25 screw for the Tee
Cut the head off the screw.
Used some blue locktite to lock it in place.
Use some blue locktite on the M3x2.5 set screws when attaching to the motor. I did have to drill out motor shaft hole to about 1/2" to avoid the set screws binding on the base plastic.
I had to enlarge the hole on the plate(s) to abut 9.10mm to fit this coupler.
This was a just a quick test of the collator for 9mm, all fed the case head down in a dozen or more tests of it.