Update april 2023:

The Bambu Lab X1C and P1P are printing more secure as my Prusa's so I've minified the tolerances to make it print great for printing at the Bambu Lab X1C and P1P

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I had some problems using the otherwise great Masterspool and I made my own variant for use with refill filament.

The existing Masterspool was a little too tight for use with Fiberlogy Refill filament. In my design I have a little bit more space and better dimensions.

I also found it difficult to print the thread neatly at a higher layer height with the original V4. I chose to make a design without threads and to provide it with a snap lock. So you can literally tighten and loosen the coil in no time at all. Nice and fast.

A third advantage of this design is symmetry. A full Masterspool consists of 2 equal halves that are easy to print. In the unlikely event that one side breaks, you only need to print 1 half.

There is a space saved where you can stick a label. The size is ideal for Avery 3657 (48.5 x 25.4 mm) and L7654-100 (45.7 x 25.4 mm.)

Finally, you need a little less filament and time to print a complete spool.