Hello, I like the idea of having a master spool, but after looking at the comments saw that this design could use a stackable feature. So I made two triangular gooves (~3mm base), one cut (part 1) and one protruding (part 2). This should aid in the stackability of these master spools. I mainly did this as a reference to help dasfilament so they can create their own version with the source files.

As for printing I have not tried this yet. I am not sure if the model has errors as I modified the current stl files and not the source files. Also not sure if the grooves will be big enough to lock. So good luck.