3d printed threads and snap connectors are nice, but M3 bolts and nuts are more robust and look dope. They also make the model easier todesign print, since you don’t have to worry about tolerances as much.
STEP/STL and instructions available here: www.printables.com/model/548770-master-spool
Variation in refill winding diameter really put me off the master spool concept a few years ago. I printed a well reviewed spool, bought a refill, and the refill was wound around a smaller radius than the spool so it wouldn’t fit. Sounds like that hasn’t changed much?
Fuck any manufacturer who makes their own standard. We have one. We don’t need a new one. Vote with your wallet. Unless the manufacturer specifies they are compatible, don’t buy it. Simple and easy.