Does anyone know what these grooves are for? Is the edge of the filament spool supposed to inside them?
They are the spool locating points.
You place the spool into the slots using those positions to help keep the spools straight when they spin.
It helps spools that are thin not to wobble.
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Yes, the spool side must be between them.
That’s why the permanent filament clips like mine (below) need to be installed in the right side of the spool.
Shameless self promotion (sorry but I really like this clip):
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