I just made spools with a 1/8th hole and then used a glue gun to fill the hole with glue and stuffed it on the motor. The motor has flats that are about 40% of the cross section.
It’s holding out pretty well but I’m concerned about it.
I’ve been back-grounding this problem for the past few days and it came to me today.
About 10 years ago I used to fly RC planes and they have collars with set screws that hold the wheels on (a few other uses too). Those parts are readily available. The picture above are Great Planes 1/8″ wheel collars. I’ll probably get some of those.
I will replace the set screw with a longer one. Then in the spool design there will be a key channel where the screw goes inside the spool.
Come think of it, a chunk of metal with a 1/8th hole drilled would work. Only problem I’d need to make some very small threads to get the set screw installed.