[Update: 1 January 2021]
base-v3.stl was provided for better mechanical stability of rolling.

[Original post]

I always wanted to have a universal filament mount of ultra-low profile with a no-bearing but smooth operation. My solution here is to use the paper clips as the rotation shaft, so that it comes with several advantages without any known problem (so far):

1. it's rotational friction is even smaller than the bearing. This is because of the smallness of the shaft's radius (0.4 mm) so the torque contributed from the friction between the shaft and the holder is very tiny that the force required to drive the roller (of radius 14 mm) is 35 times smaller than the friction;

2. it's profile is very low (about 37 mm);

3. it's cheap (because no bearings are required).

A few reminders. About the metal shaft, I used pliers to cut out a straight piece of the paper clip (see picture) and push it into the tiny axis hole of the roller. I found it useful to sharpen the shaft a bit before pushing it into the hole. You need four pieces of metal shafts (from your paper clips). When done with the shafts, I trimmed the shafts after mounting the rollers onto the base.

When you put your filament spool onto the thing and try to rotate it, you'll see when I meant by the torque argument above.

The holders on the mount is specially designed that it creates least possible friction while tolerating the inaccuracy in the dimension of the 3D prints. The tiny complex on the top is the trick so you may want to print the mount out with a resolution better than 0.1 mm.

If you hear occasional noise while rotating the spool, it's likely from either the contact between the shafts and the mount or the contact between your spool and the roller. If the former, a tiny bit of grease should be able to easily resolve the issue, although I've never heard any noise in my case. If the latter, you could wrap your roller surface with sellotapes to reduce the surface static friction that sometimes squeaks depending on the material of your spool.

I'm now working on a similar version where no paper clips are needed, i.e. to 3D print the shafts instead of using the paper clips here. This requires a bit of engineering and tests so I'll put the new design on when ready.

Do give me some feedback about your experience in this version. Have fun!

PS: If you're an FLSUN user like I'm, the two screw holes are for you to mount it on the top of the printer. These holes are designed to fit the existing screw holes and screws on the printer. If you're not an FLSUN user, you could simply ignore the two screw holes on the mount.