Some of the eSUN refilament rolls have 80 mm inner diameter and some of them have about 90 mm inner diameter. There are some nice filament spools to be printed for the refill rolls, for example the one created by Lu123. It has been designed for a smaller 80 mm roll, so it needs some spacer to fit the roll that has 90 mm inner diameter. With this adapter it fits nicely.
This seems to fit also on a FrontierFila spool.
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The author marked this model as their own original creation.