Class M and Class L (large) bobbin storage that fits into the standard tray that's on most industrial sewing machine tables.
Two versions - a 2-row, 16-spool holder and a 3-row 25-spool holder that has an integral thumb-grip for lifting the spools out or sliding them in the drawer.
Both versions print fine at .3mm resolution as there is no-need to print this with any finer detail.
2022-05-09: Added a 4-row holder, which holds 34 bobbins and is balanced better. Note: the front corners are a bit small for a bobbin which is why they are not counted in the total spaces!! My math is not that bad :-)
2022-05-15: A friend asked for a larger Class L version for his Adler 867 - so I added a design for that one as well. Holds 30 bobbins!
The author hasn't provided the model origin yet.