Prusa Core One modular ball bearing spool holder with metal axle

Prusa Core One modular ball bearing spool holder with a metal axle to prevent bending (when active temperature control is used)

Filament spool measures: Inner diameter 51 - 73mm, width 38 - 80mm

Update 12. October 2025: To clarify which parts should be downloaded/printed, I've reorganized the files and deleted the 52 mm inner diameter versions. They are replaced by the 51 mm inner diameter versions (used at Prusament spools). New is an extra wide step nut for filament spools with a width of more than 80mm. 

Use the .3mf files if you like to use some parameter presetting, use the .stp files if you like to setup the parameters by yourself.

Developing an auto rewind spool holder for the core one right side spool box, i used the model from jmillerfo as a base.

The auto rewind spool holder, building on this base, is available now.

The dual PTFE path from the spool holder, to be seen on the main picture, is available here.

The first step was to add a mount for the core one, change to a sturdy metal axle and add modular fixations for a wide range of spools. The result is this modular ball bearing spool holder.

Printing instructions:

Use PETG for all parts exept the mount, i recommend a more heat resistant filament like PETG-GF or PETG-CF for the mount plate.

Print the hub with random seam position, otherwise you have to remove the seam by hand for smooth operation!

0.4 nozzle, 0.2 structural, 3 perimeters

For easy slicer setup use the *.3mf files (most settings included)

Not printable Parts needed: 

4 x M3 hex nuts (maybe there are some spare available form the kit upgrade

1 x M6 thin hex nut (sample)

1 x M6 Flat Head Screw 75mm long (sample)

2 x 608 ZZ Ball Bearing (sample)

Optional for the every spool nut: 3 round neodym magnets 6x2mm (sample)

Assembling instruction:

Be aware that the printed M6 thread of the inner and outer fixing nut may not be easy to screw on. I recommend recutting with a thread cutter.

Take the Mount and push the 4 M3 hex nuts into the intended openings. If you have a problem with pushing in, use an M3 screw and push it from the mounting side (flat side) through the hole, screw the nut on and now drag the nut into the recession using the screw force until it's fully in. 

Now take the thin M6 nut and push it into the recession on the same side, press the mount against a table to make sure the nut is fully pressed in.

Take the M6 flat head screw and screw it into the mount from the flat side. Tighten the screw by hand, do not apply exessive force. 

Now take the inner-bearing-seat and push a 608zz bearing into the recession until it sits firm.

Put the inner-bearing-seat assy onto the mount until the bearing touches the thin hex nut. Check the space between the mount and the seat part, it should be about 1mm, depending on the width of the used nut. If the space is less than 1mm use a thin (1mm) M6 washer and put it onto the thin hex nut to get more space.

Screw the inner-fixing-nut on until the bearing seat is fixed on the screw, use a 13mm open-end wrench (prusa kit tool), do not apply exessive power.

Now push the three 14mm spacers over the screw end.

Take the hub and push the second 608zz bearing into the intended recession until it sits firm.

For easier assembly, attach the mount assy to the core one spool box wall with the four screws from the existing spool holder.

Put the hub over the assembly, make sure the teethed inner bearing seat part drops into the recessions on the hub! Fix the hub with the outer-fixing-nut by hand, then use the prusa flat-nose pliers and carefully fasten it.

If not already done, you can fix now the whole assy to the core one, using the original four screws from the spool holder.

That's it, you have successfully assembled the spool holder with bearings.

Now for the Accessories:

Push the step-ring onto the hub with the flat side to the back, use the desired step-nut to fix a spool on the holder. 

The wide nut is for up to 8mm wider spools or rotated 180 degrees for very narrow spools! 

See picture below for the step nuts and the approximate spool width they are covering

Observe how it works :)

Developing an auto rewind spool holder for the core one right side box, i used this model as a base.

The first step was to add a mount for the core one, change to a sturdy metal axle and add modular fixations for a wide range of spools.