Bambu Labs Reusable Spool for Mini-sized print bed (18cm)

You'll need the two files - the inner-tabs STL file and the outer-tabs STL file.  These two pieces latch together in a bayonet-style mating to form the reel.  

Haven't tried with other versions of the reel-less filament products, but this worked well for a roll of Bambu PLA matte I bought recently. 

An added bonus is that the flattened edges mean you can rest the spool on edge without it rolling away - might be useful for storing multiple spools on a shelf! 

The Torbenberger model was used but with the N,S,E and W edges truncated, then bridged for continuity and the vertices around those areas were cleaned up and sharp edges avoided. The result is that it will print on an 18cm square build surface, like that on the A1 Mini.  

The bayonet fit seems to be nice and snug, and the notch alignment to the Bambu reel-less filament spool is good too. 

The original design has a huge excess of vertices so a small amount of vertex merging was done, and the manifold errors subsequently cleaned up. Prints nice and clean.