YASH - Yet Another Spool Holder (compatible with IKEA 365)

With this design I was aiming for:
- simplicity
- modular application (either loose or fixed in a box )
- short printing time
- compatible with IKEA 365 boxes (10.6 litre, widely available)
- spool width up to 7cm (in an IKEA box)
- grooves on the rollers keep spools in line

Required metal parts:
- ball bearings: 5x11x5mm (685 ZZ)
- M5 screws (best countersunk, 25~30mm for single carrier, 45~50mm for double carrier)

Assembly - Spool holder for one spool:
4x Rollers
4x M5 screws (25~30mm, no nuts needed)
4x Ball bearings
2x Single carrier

Assembly - two holders in an IKEA 365 box (10.6 litre):
2x single holders as explained above (outer holders)
4x Rollers
2x M5 screws (45~50mm, no nuts needed)
4x Ball bearings
1x double carrier (centre piece)
2x ground carrier (holds the spools holders, fit IKEA 365 boxes)
Optional: glue carriers in place, use sticky pads to fix the ground carriers in the box (best at the outer edges since the boxes are slightly bent at the bottom)

Remark on the bearings:
Although it's enough to put only one bearing in each roller, this might turn out a bit shaky due to the wider dimensions of the rollers. You can also use two bearings in each roller to counter that.