I designed this universal multi spool holder set for the A1 Mini.  I believe that this type of spool holder is superior in every way to other spool holder designs. The friction of 6 608 bearings is just the right friction to allow smooth feeding but not too little to allow for runaway feeding when pulled too hard.  It accommodates for the annoying spools with larger than standard diameter and also thicker or even larger diameter normal spools. It also prevents the filament from slipping around the holder base if there is too much slack and tangling around it which has caused me many interrupted prints. I also think that removing and inserting the spools in place is easier than a standard spool holder. 

This design allows 3 additional spools to be held for a total of 4 with the existing factory spool holder.   You do not need to make any modifications to your printer. It simply slides on top and you're good to go. 
 

Watch the build and setup: [https://youtube.com/shorts/v7gz_-OAoGU](https://youtube.com/shorts/v7gz_-OAoGU)

Note:
I recommend printing the cylindrical bearing “roller” out of PETG to reduce creep. PLA worked well for about 6 months and then they got loose. I have not had the problem since I switched to PETG.

Parts:

You'll need 6 608 bearings for each filament holder mechanism.  You can use it with just one or two filament holder mechanisms. Up to 18 bearings for all 3. I got 16 of the 18 bearings from an old pair of roller blades.

You'll need a bunch of 25mm long drywall screws with an 8mm diameter head.  They are fairly standard. Just make sure the screw head doesn't fit through the 608 bearings. You might be able to get away with slightly different dimensional screws, but I've only tested with the ones pictured.

8x screws for the base and filament grippers/ptfe holder
8x screws for each spool holder mechanism

32x screws in total.

Optional 2x M3x8 screws for gripping the ptfe tube and for an emergency stop for the spool holder mechanism. 

1x PTFE Tube