This insert is designed for flexible TPU to house 18 Bernina type Bobbins in a Plastic Case (135 x 80 x 30mm - I used one from Ali express item No 4001212027744). The insert should slightly grip the Bobbins to keep them in place.

I used Esun TPU 95A with 2 perimeters, 3 solid layers top/bottom and 10% grid infill. I did get a fair bit of stringing which i had to clean up post print.  The insert may be better with use of a more flexible material but with my MMU filament path TPU 95A is all I can get to work.